Read this first: Codes and exact wording vary by model, control board, and firmware — always match the code on your unit's display and consult the unit's manual. Any gas, combustion, flue/venting, flame-sensing, overheating, or low-water fault should be handled by a licensed technician. When in doubt, turn the system off and call Phillips Hydronics at (385) 234-1916.
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Triangle Tube
Prestige and Solo models show codes like 'E-02' (hard lockout) and 'b-26' (soft lockout). The Challenger combi line uses a different single-digit display (e.g. E1/E5 = no flame, E6 = poor flame) — confirm the exact digit on the unit.
| Code | What it means & what to do |
|---|---|
| E-02 | Failed ignition lockout — tried to light and could not prove flame after 5 attempts. Common causes: Gas off or low pressure; dirty/cracked ignition or flame-sense electrode; loose gas-valve cable or poor ground; air in the gas line (common after gas work or a new LP tank). What to do: Confirm gas is on (other gas appliances work, LP tank not empty), then press RESET once. If it relocks, stop — call a licensed tech. Do not keep resetting a gas-ignition lockout. |
| E-04 | Loss of power after a lockout — power was interrupted while already locked out, so the original code was lost. Common causes: Power flicker/surge or unstable voltage; reverse polarity or poor ground on the 120V supply; someone power-cycled the boiler instead of using RESET. What to do: Press RESET once on the display (not the main power switch). If E-04 keeps returning, call a tech — the underlying lockout and power quality need diagnosis. |
| E-00 | Flame detected before ignition — control senses a flame signal when there should be none. Common causes: Gas valve leaking by / not closing fully; poor combustion; wrong/misseated LP orifice; faulty flame-sense circuit. What to do: Safety/gas-integrity fault — call a licensed tech. Do not run the boiler; it needs a combustion test. |
| E-12 | External limit lockout — a safety limit wired to the boiler (or the factory jumper) is open. Common causes: External high-limit or low-water cutoff tripped; factory jumper missing/loose; broken internal wiring; real over-temp or low-water condition. What to do: Press RESET once. If it immediately returns, call a tech — an open safety limit can mean a genuine over-temp or low-water problem and must not be jumpered out. |
| E-18 | High temperature limit (supply) — outlet water exceeded 212°F and hard-locked out. Common causes: Low or no flow (failed/wrong circulator, closed valve); air trapped in the system; stuck pump; faulty supply sensor. What to do: Check that pressure reads ~12–15 psi and circulators are running/warm; bleed obvious air if you know how. Press RESET once. If it recurs, call a tech — repeated overheating isn't safe to ignore. |
| E-25 | Supply temperature rose too rapidly (very low flow), then hard-locked out. Common causes: Low/no flow (undersized, failed, or air-bound circulator); air not purged; closed isolation/zone valves; demand far below the boiler's low-fire output on a small single zone. What to do: Verify pumps run and pressure is ~12–15 psi; bleed air if comfortable. Press RESET once. If it returns, call a tech — almost always a circulation problem. |
| E-52 | Flue temperature exceeded 250°F and locked out (warnings b-40/b-52 often appear first). Common causes: Sooted/scaled heat-exchanger flue passages; scale inside the heat exchanger; faulty/mis-positioned flue sensor; combustion or venting problem. What to do: Call a tech. High flue temperature usually means the heat exchanger needs professional cleaning or there's a combustion problem — not a homeowner fix. |
| E-31 / E-32 / E-36 / E-37 | Boiler temperature sensor fault — supply (S1) or return (S2) sensor reads shorted (E-31/E-32) or open (E-36/E-37). Common causes: Loose, corroded, or damaged sensor wiring/connector; failed supply or return sensor; pinched wire; moisture in a connector. What to do: Internal sensor/wiring fault — call a tech to inspect and replace the affected sensor. |
| E-28 / E-29 / E-65 | Blower (fan) fault — control isn't seeing the blower run correctly (E-28/E-65) or it runs when it shouldn't (E-29). Common causes: Failed/seized blower motor; damaged or loose blower wiring; loss of fan supply voltage; faulty control module. What to do: Call a tech. Blower diagnosis requires checking voltages at the connector — not a homeowner step. |
| b-26 | Soft lockout — Low Water Cut-Off is open (low water / low pressure). Auto-resets ~150 sec after corrected. Common causes: System pressure too low (below ~10 psi); leak or failed/empty make-up valve; failed low-water cutoff or open wiring; air-bound system reading low. What to do: Check the gauge — should read ~12–15 psi cold. If low, look for visible leaks and check the fill valve. If you can't safely repressurize, or pressure keeps dropping, call a tech (recurring low water points to a leak). |
| b-18 / b-19 | Soft lockout — high temperature limit on return (b-18) or supply (b-19). Burner pauses until water drops below ~200°F, then resumes. Common causes: Heat demand lower than the boiler's minimum output; low flow or restriction; air not purged; drifting supply/return sensor. What to do: Often self-clears. Confirm pumps run and pressure is ~12–15 psi. If it repeats, call a tech to look at zoning/flow and sensors. |
| Challenger E1 / E5 / E6 | Challenger combi: E1/E5 = no flame signal at ignition; E6 = weak flame signal. Red LED above RESET flashes. Common causes: Manual gas valve closed or air in gas line; low gas pressure; wrong ignition gap, bad ignition cable/cap, or failed ignition unit; blocked condensate drain. What to do: Confirm gas is on and other gas appliances work, then press RESET once. If it relocks, stop and call a tech — gas pressure, ignition, and combustion are professional checks. |
Source: manufacturer documentation
Lochinvar
Knight boilers with the SMART SYSTEM / SMART TOUCH control display text fault MESSAGES (e.g. 'No Flame Ign', 'Fan Low'), not numbered codes. Exact wording varies by firmware/model year.
| Code | What it means & what to do |
|---|---|
| No Flame Ign | Ignition failure / lockout — failed to prove ignition after four attempts. Common causes: Dirty/misaligned spark or flame-sense electrode or poor grounding; low or interrupted gas (NG 4–14" w.c., LP 8–14" w.c.); blocked/improper vent or disconnected gas-valve sensing hose; failed gas valve or board. What to do: Confirm gas is on and press RESET once. If it lights and stays lit, monitor. Don't repeatedly reset a gas-ignition lockout — if it relocks, call a pro to check electrode, gas pressure, venting, and gas valve. |
| No Flame Running | Flame loss — boiler was running and lost the flame signal four straight times, then locked out. Common causes: Dirty/failing flame-sense electrode or poor grounding; marginal/fluctuating gas pressure; vent/air-intake obstruction or condensate/flue problems; failing gas valve or board. What to do: Press RESET once and watch whether it stays lit. Recurring flame loss is a gas/combustion issue — call a qualified tech. Don't keep resetting. |
| Gas Pressure SW | A manual-reset low- or high-gas-pressure switch has tripped. Common causes: Incoming gas pressure out of range; partially closed gas valve, regulator problem, or undersized gas line; tripped switch; loose/misplaced jumper. What to do: Verify the building gas valve is fully on and other gas appliances work, then press RESET once. Gas-pressure measurement/adjustment must be done by a pro with a manometer. |
| Flow Switch/LWCO | Flow switch or low-water cutoff isn't detecting adequate flow/level. Common causes: Boiler pump not running on a call for heat; closed isolation valves or obstruction; air in the system; blown board fuse or missing jumper. What to do: Check that system pressure is adequate (~12+ psi) and listen for the circulator. Bleeding air, fuses, and pump diagnosis should be done by a tech. |
| APS Open | Air pressure switch open — control isn't seeing proper combustion-air/draft proving. Common causes: Vent/intake exceeds maximum length; obstruction in the vent/intake or terminations; blocked/disconnected pressure-switch hoses; dirty burner/heat exchanger or failed switch. What to do: Flue/combustion-air system — call a tech. Homeowners can confirm exterior intake/exhaust aren't blocked by snow, ice, leaves, or nests; internal diagnosis is a pro job. |
| Auto Reset High Limit | Outlet water temperature exceeded the high-limit setting. Common causes: System not full / air not purged, or low flow; circulator not running or failed; improper piping; faulty sensor or high-limit device. What to do: Confirm pressure is normal and the circulator runs. Low-flow/overheat conditions and sensor/pump replacement should be handled by a tech, especially if it recurs. |
| Fan Low / Fan High | Combustion-fan RPM is ~30% lower or higher than commanded. Common causes: Vent/intake exceeds max length or is obstructed; loose/damaged wiring at fan or board; failing fan; blown board fuse or failed board. What to do: Call a tech to inspect fan, wiring, and venting. Homeowners can check that exterior vent/intake terminations are clear. |
| GV/Relay Fail | The control board did not detect the gas valve. Common causes: Loose or failed wiring between board and gas valve; failed harness; failed gas valve; failed board. What to do: Gas-valve fault — call a qualified technician. Not a homeowner repair. |
| Sensor Open / Sensor Shorted | An inlet or outlet water temperature sensor reads open or shorted. Common causes: Disconnected, damaged, or pinched sensor wiring; failed sensor; corroded connection. What to do: A tech should check/replace the sensor and wiring. Generally needs a service visit. |
| Anti-cycling | Not a failure — control got a new call for heat too soon and is delaying the burner to prevent short-cycling. Common causes: Normal short-cycle protection; oversized boiler for the current load; thermostat cycling quickly. What to do: Usually no action — the burner restarts automatically after the timer. If the boiler short-cycles excessively over time, mention it at your next service. |
| Low 24 vac | 120 vac input to the control dropped too low (low/unstable supply voltage). Common causes: Low/unstable building supply; loose low-voltage wiring; undersized/too-long wiring to remote devices; failed transformer. What to do: Check the breaker and that the boiler power switch is on. Electrical-supply and transformer diagnosis should be done by a qualified tech/electrician. |
Source: manufacturer documentation
Viessmann
Vitodens 200-W / 222-F detailed fault codes. Reset is via the 'R' button. Older Vitodens 100-W may show a different set.
| Code | What it means & what to do |
|---|---|
| F2 | High-limit (fixed temperature limiter) tripped — boiler got too hot and locked out. Common causes: Low or no water flow; air in the system; failed/stuck circulator; faulty high-limit switch or wiring. What to do: Confirm pressure is in range and bleed air; make sure the circulator runs. Reset with 'R'. Repeated F2 lockouts, or pump/high-limit replacement, need a pro. |
| EE | No flame or too weak a flame signal at burner start (ignition failure). Common causes: Gas supply problem; ignition/ionization electrode fouled, mis-gapped, or miswired; blocked condensate drain; ignition module fault. What to do: Verify the gas supply is on. Gas/combustion fault — press reset once; if it recurs, call a licensed pro. |
| EF | Flame lost immediately after it lights (during the safety time). Common causes: Inadequate gas pressure/supply; flue gas recirculation or flue/air problem; contaminated or mis-gapped ionization electrode. What to do: Gas/combustion/flue issue — don't open the boiler. Press reset once; if it returns, call a pro to check gas, flue, and electrode. |
| EA | Ionization (flame) current outside the permissible range during calibration. Common causes: Flue gas recirculation; very dusty combustion air; fouled/mis-positioned ionization electrode; gas mixture/coding-card issue. What to do: Diagnostic/combustion fault — call a pro. After several failed resets the coding card may need replacement (pro task). |
| F1 | Maximum flue gas temperature exceeded the 230°F (110°C) limit. Common causes: Low water level/air-bound system; weak or failed pump; faulty boiler water temperature sensor; dirty heat exchanger. What to do: Check fill level and bleed air. Let the vent system cool before resetting with 'R'. Persistent F1 (overheating) needs a pro. |
| F9 | Fan speed too low during burner start. Common causes: Failing fan/blower; fan wiring or power-supply fault; fan control fault. What to do: Combustion-fan fault — call a pro. Press 'R' once; if it recurs, a tech should check the fan, wiring, and control. |
| FC | Gas valve faulty / faulty modulation-valve control, or vent (flue) blocked. Common causes: Defective gas valve or its control; blocked/restricted vent or flue. What to do: Gas valve and flue are pro-only. Don't operate the boiler — call a licensed technician. |
| F3 | Flame signal already present at burner start (false flame). Common causes: Ionization electrode or cable fault; control sensing a false/residual flame signal. What to do: Safety lockout — call a pro to check the ionization electrode and wiring before returning to service. |
| 30 / 38 | Boiler water temperature sensor fault — short circuit (30) or broken/open cable (38). Burner blocked. Common causes: Shorted or open boiler water temperature sensor; damaged sensor wiring/connector. What to do: Sensor diagnosis/replacement is a tech task. Call a pro if the boiler stays blocked. |
| B0 / B8 | Flue gas temperature sensor fault — shorted (B0) or open/broken cable (B8). Burner blocked. Common causes: Shorted or open flue gas temperature sensor; damaged wiring. What to do: Flue-sensor diagnosis is a pro task; call a tech to check the sensor and wiring. |
| FE | Damaged or incorrect boiler coding card, or main board fault. Common causes: Faulty/incorrect coding card; main control board fault; strong external interference. What to do: Control/board issue — call a pro. Reset may clear it; if not, the coding card or control unit needs servicing. |
Source: manufacturer documentation
Weil-McLain
Evergreen models display plain-English text messages (e.g. 'IGNITION FAULT'). Ultra models show E-codes (E02, E18) for hard lockouts and 'b' codes for soft lockouts. GV90+ uses LED flash patterns, not codes — call us to interpret those.
| Code | What it means & what to do |
|---|---|
| IGNITION FAULT | Evergreen: 5 ignition attempts with no flame detected. Common causes: Blocked condensate trap; fouled/worn/mis-gapped igniter or loose ignition cable; flue/intake restriction or recirculation; dirty burner/heat exchanger; low incoming gas pressure. What to do: Gas/ignition fault — don't service internally. It auto-resets after ~1 hour, but a no-light boiler in cold weather warrants a pro to check gas, igniter, and venting. |
| FLAME FAULT | Evergreen: flame detected when there should be none. Common causes: Incorrect combustion / burner running too hot; gas valve not fully closing (flame persists after shutdown). What to do: Requires manual reset. Combustion test and gas-valve check are pro tasks — call a technician; a leaking gas valve is a safety issue. |
| GAS VALVE FAULT | Evergreen: control detected a problem with the gas-valve output circuit. Common causes: Gas valve or its control/wiring fault; control board fault. What to do: Auto-retries; if it locks out it needs manual reset. Gas valve work is pro-only — call a licensed technician. |
| BLOWER FAULT | Evergreen: blower can't reach required speed, or won't return to 0 RPM when off. Common causes: Loose blower wiring/connector; failed blower motor; no 120V at blower; control fault. What to do: Auto-retries after ~1 hour. Blower/electrical diagnosis is a pro task. |
| LOW WTR CUTOFF OPEN | Evergreen: internal low-water cutoff contacts opened — possible low water. Common causes: Genuine low-water / low-pressure condition; fouled LWCO probe; LWCO wiring fault. What to do: Check system pressure; if low, find/repair the cause of water loss. Probe cleaning/replacement should go to a pro. |
| HIGH TEMP LIMIT | Evergreen: boiler temperature sensor reached the high-temperature limit. Common causes: Closed isolation valves or wrong circulator config; poor flow / wrong pump size; piping error; sensor issue. What to do: Verify isolation valves are open and circulators run. Requires manual reset. Repeated overheating lockouts need a pro. |
| FLUE TEMP TOO HIGH | Evergreen: flue temperature exceeded 210°F (warning) or 220°F (lockout). Common causes: Heat-exchanger/flueway buildup or wear; vent system problem; faulty flue sensor. What to do: Above 220°F requires manual reset. Heat-exchanger and vent inspection are pro tasks — call a technician. |
| TEMPERATURE SENSOR FAULT | Evergreen: a temperature sensor is shorted, open, or two sensors disagree by >10°F. Common causes: Failed sensor; loose connector/pin; damaged harness. What to do: Auto-resets when the condition clears. Sensor diagnosis/replacement is a pro task. |
| AIR PRESSURE SWITCH OPEN | Evergreen: the air-pressure-switch connection is open. Common causes: Wrong boiler size selected in the control vs. the rating label; missing/incorrect factory jumper. What to do: Requires manual reset. Settings/jumper verification is a pro task. |
| E02 (Ultra) | Ultra: hard lockout — ignition failed after 5 tries. Common causes: Gas supply problem; ignition/flame-sense electrode fault; flue/condensate issue; dirty burner. What to do: Hard lockout needs manual RESET. Gas/ignition diagnosis is pro-only; if it relocks, call a technician. |
| E18 / E19 (Ultra) | Ultra: hard lockout — outlet (E18) or return (E19) water temperature was over 210°F (overheat). Common causes: Low/no flow; air-bound system; failed circulator; sensor fault. What to do: Overheat lockout requires manual reset. Check that the pump runs and the system isn't air-bound; repeated lockouts need a pro. |
Source: manufacturer documentation
Bosch
US Greenstar (ZBR/ZWB wall-hung and FS floor-standing). Codes verified on US contractor manuals. 'EA' (flame failure on ignition) appears mainly on UK/Worcester-Greenstar literature — it may show on some Bosch units; verify against your model.
| Code | What it means & what to do |
|---|---|
| EA | No flame detected during ignition (flame establishment failure) — common flame-failure lockout. Common causes: Gas supply off or low; faulty gas valve; fouled/mis-gapped ignition or flame-sense electrode; flue/condensate problem. What to do: Confirm the gas supply is on and the system has pressure. Gas/ignition fault — don't open the boiler. If a single reset doesn't clear it, call a licensed pro. |
| E9 | Heat-exchanger safety high-limit, or flue gas temperature limiter, tripped (overheat). Common causes: Low operating pressure / poor circulation; failed pump (pump capacitor); blown board fuse; faulty high-limit; clogged DHW heat exchanger; air in system. What to do: Check system pressure. Overheat safety trip — a pro should check the limiter, pump, and heat exchanger. Don't repeatedly reset. |
| C6 | Fan not running (combustion fan fault). Common causes: Failed fan; fan wiring/connector fault; control fault. What to do: Combustion-fan fault — call a pro to check the fan and its leads. Not a homeowner repair. |
| d3 | Temperature high-limit fault / external guard tripped / temperature limiter locked out. Common causes: External temperature limiter, LWCO, or pressure regulator tripped; high-limit tripped; missing jumper across the limit terminals. What to do: May involve an external LWCO/limiter — but the cause must be found. Wiring/jumper and limit checks are pro tasks. |
| E2 | Supply (flow) temperature sensor defective. Common causes: Shorted or open supply temperature sensor; damaged leads/connector. What to do: Sensor diagnosis/replacement is a tech task. Call a pro. |
| A7 | DHW (domestic hot water) temperature sensor defective. Common causes: Shorted or open DHW temperature sensor; damaged leads. What to do: Affects hot water; sensor replacement is a pro task. Heating may still run. |
| Ad | DHW tank temperature not detected (sensor recognized, then connection lost). Common causes: Disconnected or failed DHW tank sensor; damaged lead. What to do: Check/replace the tank sensor and lead — technician task. |
| CC | Outdoor temperature sensor not recognized. Common causes: Outdoor sensor disconnected or wiring open; sensor not on the correct terminal. What to do: Generally a comfort/efficiency (weather-compensation) issue, not a safety lockout. Have an installer verify the outdoor sensor wiring. |
| b1 | Code plug not detected. Common causes: Code plug missing, not seated, or defective. What to do: Code plug needs reseating/replacement by a technician. |
| b7 | Fault in the burner controls. Common causes: Internal burner-control fault; control board issue. What to do: A tech may reset to factory default; if it persists, control replacement. Pro task. |
| A8 | Communication fault (BUS communication lost between control and accessory/controller). Common causes: Damaged or loose BUS wiring; failed accessory controller. What to do: Wiring/control diagnosis — technician task. |
Source: manufacturer documentation
HTP
HTP uses two schemes: wall-hung Elite FT / EFTC show 'Fxx' plus a text label; UFT/UFTC combi show 'Er:xx'. Confirm which family your unit is.
| Code | What it means & what to do |
|---|---|
| Er:11 / F09 (No flame on ignition) | Ignition failure — failed to light after the max tries (5 on UFT, 4 on Elite FT) and locked out. Common causes: Gas off/low pressure or air in the line; spark electrode fouled or wrong gap; igniter/transformer wiring loose; flue or condensate blockage. What to do: Verify the gas valve is open; one reset is OK. Don't keep resetting — a tech should check gas pressure, clean/re-gap the electrode, and inspect venting. |
| Er:10 / F10 (Flame loss) | Flame loss — boiler lit, then lost flame repeatedly during firing. Common causes: Low/fluctuating gas pressure; dirty or grounded flame sensor; blocked condensate trap or flue recirculation; poor grounding. What to do: Confirm gas is on and try one reset. If it returns, stop and call a pro to check gas pressure, the flame sensor, and the flue/condensate line. |
| F11 (False flame signal) | Elite FT: control detects flame when the boiler isn't supposed to be firing. Common causes: Gas valve leaking by / not closing; flame-rectifier or spark probe shorted; condensate backup; damaged refractory grounding the probe. What to do: Call a pro immediately. Gas-safety fault — a leaking gas valve must be diagnosed and replaced by a qualified technician. |
| F00 (Water high temp) | Elite FT: boiler water overheated; hard safety lockout. Pump runs to cool down. Common causes: Circulator not running or wrong valves closed; no/low flow; air-bound system; failed water high-limit sensor. What to do: Safety lockout — call a pro to find why it overheated (flow, pump, sensor). Don't bypass the high-limit. |
| F01 (Flue temp / water level) | Elite FT: flue temperature limit tripped OR low water level (if a low-water cutoff is installed). Hard lockout. Common causes: Excessive flue temperature (combustion mis-set, blocked/damaged flue, cracked target wall); genuine low-water condition. What to do: Flue/combustion and low-water safeties = call a pro to clear the fault and correct the root cause before resetting. |
| Er:16 (Overheat) | UFT/UFTC: operating sensor detects water above 203°F (95°C). Common causes: High-fire dip switches set wrong; blocked DHW inlet / low flow; failed DHW or operating sensor. What to do: Self-clears as water cools (pump runs to cool the boiler). If it recurs, call a pro to check flow and sensors. |
| F02 / F03 (Supply / return sensor) | Elite FT: supply (F02) or return (F03) temperature sensor failed; lockout. Common causes: Failed thermistor; damaged/loose sensor wiring or connector; no 5 VDC to sensor. What to do: Sensor replacement is a tech task. Boiler won't restart until the sensor is replaced and RESET is pressed. |
| Er:20 (Condensate) | UFT/UFTC: condensate trap/switch open (should be closed). Common causes: Blocked or disconnected condensate hose; clogged condensate line/termination; failed switch; blocked exhaust vent. What to do: Check the condensate hose is connected and not clogged/frozen. If clearing the line doesn't fix it, call a pro (vent/condensate blockage can be a flue-safety issue). |
| Er:29 (Air pressure switch) | UFT/UFTC: air pressure switch open when it should be closed. Common causes: Disconnected/damaged switch hose; blocked condensate line or exhaust vent; failed switch; loose connections. What to do: Often points to a vent/exhaust blockage — treat as a pro call to check the switch, hose, condensate line, and flue. |
| LOU (24 volt low) | Elite FT: the control's 24-volt supply is low/overloaded. Auto-resets if temporary. Common causes: Line voltage out of range (must be 100–128V); shorted external sensor/LWCO wiring; gas valve drawing excess current; failed board. What to do: Check that the boiler has normal house power. If it persists, call a pro — a shorted harness or failed board is a tech task. |
Source: manufacturer documentation
IBC
IBC uses different controllers: SFT/SFC show 'Fxxx' codes; older DC-series show short numbers (1, 4, 5, 8, 18, 19, sensor groups 10–14 / 20–24); newer SL 'G3' boilers show plain-text messages on a touchscreen. The code you see depends on your controller.
| Code | What it means & what to do |
|---|---|
| F004 / display 4 (No flame at start-up) | Boiler did not establish flame on start-up / ignition failure. Common causes: Manual gas valve closed or line not purged; gas inlet pressure below ~4"; gas valve or igniter not powered; poor grounding; blocked condensate drain. What to do: Confirm the gas valve is open; one reset is OK. If it repeats, call a pro to check gas pressure, igniter, and grounding. |
| F005 / display 5 (Flame lost during operation) | Flame established but lost during firing (poor/dropped flame signal). Common causes: Blocked condensate drain; gas pressure too low or drooping under load; gas valve adjustment; flue/air recirculation or blockage; poor grounding. What to do: Combustion fault — call a pro to check gas pressure under load, flame sensor, grounding, and flue/air piping. |
| F003 / flue sensor 18-19 (Flue gas temp too high) | Flue gas temperature exceeded its limit (or flue sensor open/short on DC). Common causes: Contaminated/fouled heat exchanger; flue sensor fault or wiring. What to do: Call a pro. Excess flue temperature usually means the heat exchanger needs cleaning — a combustion/flue issue. |
| F008 / display 8 (Incorrect fan speed) | Combustion fan not running at the commanded speed. Common causes: Fan cable loose; fan rubbing the casing; failed fan; board fault. What to do: Call a pro. Fan/combustion component — a tech should check or replace the fan. |
| F010 / F011 (Heat-exchanger sensor S0) | Heat-exchanger temperature sensor (S0) out of range / open or shorted. Common causes: Broken or disconnected S0 wiring; sensor not seated; failed sensor. What to do: Tech task — check wiring and replace the heat-exchanger sensor. Not a homeowner repair. |
| DC 10–14 / 20–24 (Supply S1 / return S2 sensor) | Supply (S1) or return (S2) temperature sensor out of range; boiler won't light. Common causes: Sensor mis-positioned; wiring break; failed sensor. (Can appear briefly on a very cold start.) What to do: If it appears on a very cold start it may clear as the unit warms. Persistent S1/S2 faults need a pro to test/replace the sensor. |
| DC display 1 (Temperature too high) | Boiler water temperature too high / overheat hold. Common causes: Air in system; pump not running or air-bound; insufficient flow (closed radiators/valves); restricted circulation. What to do: Confirm the system isn't air-bound and zones/valves are open. If it persists, call a pro to bleed/check the pump and flow. |
| F018 (Flue/air duct blocked) | Air-intake and/or flue (exhaust) is obstructed. Common causes: Blocked, iced, or debris-filled intake/exhaust terminal; sagging or disconnected vent piping. What to do: Check the outside vent terminals for snow/ice/debris and clear obvious blockage. Internal vent work and re-light = call a pro (flue safety). |
| SL: Ignition Failure after 3 tries | SL touchscreen: failed to ignite on 3 attempts; 1-hour lockout, then retries. Common causes: Ignition lead/flame sensor loose; gas shutoff closed or line not purged; wrong spark gap; spark but no gas-valve power; poor grounding. What to do: Confirm gas is on; one reset is fine. Repeated ignition failure = call a pro. |
| SL: Water High-Limit Exceeded | SL touchscreen: water temperature exceeded the high limit; hard lockout. Common causes: Loss of flow (pump off/air-bound, closed zones); failed sensor; over-firing. What to do: Safety lockout — call a pro to find the cause of overheating before resetting. Don't bypass the high limit. |
| SL: Low Water Cutoff | SL touchscreen: low-water condition detected; boiler in lockout. Common causes: Low system pressure/water level; air in the boiler; LWCO probe issue. What to do: Check system pressure on the gauge. If low water/pressure persists or you're unsure, call a pro — low-water is a safety lockout. |
Source: manufacturer documentation
Laars
NeoTherm (Honeywell SOLA touchscreen) shows numeric codes plus plain-text in an orange status bar. Codes 1–62 are mostly internal/sensor self-checks; everyday lockouts (ignition failed, flame lost, high-limit) appear as TEXT in the status bar. Mascot FT and older Mighty Therm use different schemes — call us.
| Code | What it means & what to do |
|---|---|
| 63 (Safety chain / rollout) | A device in the safety chain opened: flow switch, extra high-limit, low-water cutoff, low/high gas-pressure switch, or condensate level switch. Common causes: Tripped low- or high-gas-pressure switch; low water/low flow; tripped high-limit; full or blocked condensate; loss of power at the safety terminal block. What to do: Call a pro to identify which safety device opened and correct the root cause. Gas-pressure and low-water trips are not homeowner resets. |
| 61 (Anti short cycle) | Normal protective hold — the burner is held off to prevent rapid on/off cycling. Not a fault. Common causes: Frequent short demands; oversized boiler for the load; normal delay between cycles. What to do: No action usually needed — it clears itself. If the boiler short-cycles constantly, have a pro review sizing/controls. |
| 62 (Fan speed not proved) | The combustion fan didn't reach the required speed during start. Common causes: Fan wiring/connector issue; failing fan; obstruction; control fault. What to do: If it persists, call a pro to check or replace the combustion fan. Not a homeowner repair. |
| 51 (Pump fault) | Control detected a problem with the boiler pump/circulator subsystem. Common causes: Failed or stalled pump; wiring; flow problem. What to do: Have a pro check the circulator and flow. A boiler that can't move water shouldn't be run hard. |
| 49 (24 VAC voltage low/high) | The control's 24 VAC supply is outside the acceptable range. Common causes: Transformer/power-supply problem; loose module or display connections; supply voltage/frequency out of spec. What to do: Pro task — check the transformer, connections, and incoming power. |
| 53 (AC input phases reversed) | Line and neutral reversed / wiring polarity problem on the AC input; lockout. Common causes: Reversed line/neutral wiring; on 24 VAC applications, a missing jumper. What to do: Call a pro/electrician — incorrect AC polarity must be corrected by a qualified person. |
| 3–31 (Internal fault) | Family of internal control-module faults (hardware, safety-relay, flame-bias, spark-voltage self-checks). Common causes: Transient electrical disturbance or a failing burner-control module. What to do: Try one reset. If an internal-fault code repeats, the control module typically must be replaced by a technician. |
| 1 / 2 (Safety data not verified) | The control needs its safety parameters verified — usually after a control/module replacement or a safety-parameter change. Common causes: New/replaced control module not yet verified; a safety parameter changed without completing verification. What to do: Installer/technician task — complete the device configuration and safety verification. Not a homeowner step. |
Source: manufacturer documentation
NTI
Trinity Tft/TFTN (Honeywell SOLA) show bare numeric codes (e.g. 110). Trinity Tx/FTV (Argus display) show 'Loc' lockout and 'Err' blocking codes. Numbering does NOT map across the two — identify yours by whether the display shows a bare number or a 'Loc'/'Err' prefix.
| Code | What it means & what to do |
|---|---|
| 110 (Tft) | Ignition failure — tried the max times and couldn't light or hold flame, so it locked out. Common causes: No/low gas (closed valve, LP low, regulator); blocked vent/intake or plugged condensate trap; dirty/failed flame sensor or electrode; reversed polarity or weak ground. What to do: Confirm gas is on and the thermostat is calling, then press Reset once. If it locks out again, stop and call a licensed technician. Never repeatedly reset a boiler that won't light. |
| 67 (Tft — ILK OFF) | Safety interlock open — a device in the interlock loop (low-water cutoff, external high-limit, blocked-vent/air switch) tripped or lost continuity. Common causes: Tripped low-water cutoff from low pressure; tripped external high-limit; loose/broken wire; blocked-vent or air switch tripped. What to do: Check that system pressure is ~12–25 psi. Beyond confirming pressure, an open safety interlock should be diagnosed by a tech. Do not bypass. |
| 79 (Tft — outlet high limit) | Supply water temperature exceeded the high-limit setpoint. Common causes: Poor flow (closed valve, stuck/failed circulator, air-bound); clogged strainer or fouled heat exchanger; set temp too high; faulty outlet sensor. What to do: Make sure valves are open and the circulator runs; bleed obvious air if you know how. If it keeps tripping, call a pro. |
| 81 (Tft — Delta-T limit) | Temperature difference between supply and return is too large — inadequate flow. Common causes: Undersized/failing circulator; air-bound or closed valve; clogged strainer/dirty heat exchanger; too little flow for the firing rate. What to do: Confirm the circulator runs and valves are open. Persistent delta-T limits are a flow problem — have a tech verify pump sizing and purge air. |
| 91 / 92 / 93 (Tft — sensors) | Temperature sensor fault: 91 return, 92 supply, 93 domestic hot water. Out-of-range reading. Common causes: Loose/corroded connector; damaged/pinched wiring; failed thermistor; moisture in the connector. What to do: No homeowner action beyond one reset. A failed sensor needs a tech to test and replace the specific probe. |
| 100 (Tft — pressure sensor) | Control sees an invalid reading from the water-pressure sensor. Common causes: Genuinely low system pressure; loose/failed pressure sensor or connector; damaged wiring; air or debris. What to do: Check the gauge — if under ~12 psi the system may need topping up by someone familiar with the fill valve. If pressure is normal, the sensor is suspect; call a pro. |
| Loc 1 (Tx) | Ignition error — repeated unsuccessful ignition attempts; locked out. Common causes: Blocked venting or plugged condensate trap; insufficient gas / regulator problem; dirty/failed flame sensor or electrode; reversed polarity. What to do: Confirm gas is on and press Reset once. If it locks out again, stop and call a technician. |
| Loc 5 (Tx — limit/safety) | A safety-limit device opened: external limit/low-water cutoff OR the internal heat-exchanger thermal fuse opened from overheating. Common causes: Tripped external limit/LWCO; heat-exchanger thermal fuse opened (low flow); loose connection; low water/poor circulation. What to do: You may check system pressure, but an open limit/thermal fuse must be investigated by a technician. Do not bypass. |
| Loc 12 (Tx — fan speed) | The blower isn't reaching target speed within ~60 seconds. Common causes: Loose fan wiring; failed blower; blown inline blower fuse; obstruction. What to do: Not a homeowner repair. Call a technician to check blower wiring, fuse, and motor. |
| Loc 27 (Tx — flame out of sequence) | Control still senses flame ~10 seconds after the gas valve closed. Common causes: Flame sensor reading incorrectly; blocked condensate drain; slow-closing or leaking gas valve; post-purge too short. What to do: Safety-related flame-sensing fault. Call a licensed technician — gas valve and flame-detection issues are not homeowner repairs. |
| Err 65 (Tx — polarity) | Control detects reversed 120V line/neutral. Common causes: Line and neutral swapped at the boiler, outlet, or junction; miswired field connections; poor grounding. What to do: Electrical wiring fault — correct by a qualified electrician/technician. Common on new installs or after electrical work. |
Source: manufacturer documentation
Burnham
Burnham Alpine: newer units (Sage 2.1 control) show a plain number + text (read via the 'Help' button); older units (MCBA control) show 'E'+code hard lockouts and '9'/'b'+code soft lockouts. The cast-iron ESC line has no digital fault display.
| Code | What it means & what to do |
|---|---|
| 11 (Sage) / E 02 (MCBA) — Ignition failure | Failed to light/prove flame after the allowed attempts (hard lockout, manual reset). Common causes: No gas or pressure below the rating plate minimum; air in the gas line; defective electrode, cable, or loose burner ground; defective gas valve or air-fuel mixture off. What to do: Confirm gas is on and the boiler's gas valve is open; press Reset once. If it fails again, stop and call a licensed pro. |
| 2 (Sage) / b 08 (MCBA) — Pressure switch / blocked vent | Boiler safety/pressure switch open — commonly a plugged condensate trap or a blocked vent/intake. Common causes: Plugged condensate trap or boiler not level; air pressure switch open from a blocked vent/intake; auto-reset high limit tripped; loose wiring. What to do: Check that outdoor vent/intake terminals are clear of snow, ice, leaves, or nests, and the condensate line/trap isn't clogged or frozen. If clearing it doesn't help, call a pro. |
| 3 (Sage) / E 13 (MCBA) — External limit / LWCO | An external limit, low-water cutoff, or low-gas-pressure switch is open (or its jumper is missing). Common causes: Low-water cutoff tripped (system low on water); external limit open/defective or jumper missing; low gas pressure switch open; loose wiring. What to do: Check system pressure (~12–15 psi cold) and the LWCO light. Don't repeatedly add water — low water usually means a leak. Call a pro. |
| 1 (Sage — Anti Short Cycle) | Normal anti-short-cycle delay — minimum time between burner starts hasn't elapsed. Not a fault. Common causes: Boiler recently shut off and is waiting out its delay; frequent thermostat cycling. What to do: No action — clears within a few minutes. Only call a pro if the boiler never re-fires after the delay. |
| 14 (Sage — Delta-T high) | Supply-to-return temperature difference too high — usually low or no flow. Common causes: Inadequate flow — circulator not running or undersized; trapped air or closed valves; flow reversed; supply/return sensor defective. What to do: Confirm the circulator runs and pipes are warming; bleeding trapped air may help if you know how. If the pump isn't running or it repeats, call a pro — low flow can damage the boiler. |
| 8 (Sage — Supply sensor) | Shorted or open supply (outlet) water temperature sensor. Common causes: Shorted or mis-wired supply sensor wiring; defective sensor; loose connection. What to do: Sensor/wiring fault — call a pro to test and replace the sensor. |
| 7 (Sage — Return sensor) | Shorted or open return (inlet) water temperature sensor. Common causes: Shorted or mis-wired return sensor wiring; defective sensor; loose connection. What to do: Sensor/wiring fault — call a pro to test and replace the return sensor. |
| 4 (Sage) / E 18 (MCBA) — Supply high limit | Supply water temperature exceeded the high limit (~200–210°F) — usually low flow. Common causes: Load far below the boiler's minimum firing rate; defective circulator or no flow; control mis-wired so the boiler fires with no zone calling; air-bound or closed valves. What to do: Confirm the circulator runs and the system isn't air-bound. If it recurs, call a pro — persistent high-limit trips need professional diagnosis. |
| E 00 (MCBA — flame out of sequence) | A flame signal was sensed when there should be no flame. Hard lockout for safety. Common causes: Gas valve passing gas when it should be closed; flame-sensing fault / false flame signal. What to do: Gas-safety lockout — do NOT keep resetting. Call a licensed technician immediately to inspect the gas valve and flame-sensing circuit. |
Source: manufacturer documentation
Rinnai
I-Series condensing combi and solo boilers use E:### codes. Normal system pressure on these runs ~17–26 psi. (Rinnai tankless water heaters use a different code set — ask us if that's what you have.)
| Code | What it means & what to do |
|---|---|
| E:100 | Air supply or exhaust blockage / condensate trap full. Common causes: Blocked/frozen intake or exhaust vent (debris, snow, ice, nests); full/clogged condensate trap; disconnected or sagging vent piping; obstructed vent termination. What to do: Safely check that outdoor intake/exhaust terminations are clear of snow, ice, leaves, or debris. If clearing them doesn't resolve it, or the condensate trap needs service, call a licensed pro. |
| E:110 | No ignition — burner failed to light. Common causes: Gas off or interrupted (closed valve, empty propane, low pressure); air in the gas line; faulty igniter, electrode, or gas valve; blocked vent or condensate. What to do: Verify the manual gas valve is open and (propane) the tank isn't empty, then one reset. If it won't light or recurs, stop and call a pro. |
| E:120 | Flame failure — flame was established but then lost. Common causes: Low/fluctuating gas pressure or low propane; dirty or misaligned flame rod; poor grounding or reversed polarity; partial vent/condensate restriction. What to do: Confirm gas is fully on, then one reset. Flame-sensing/combustion faults need a tech with a combustion analyzer — if it doesn't clear, call a pro. |
| E:140 | Heat exchanger overheat. Common causes: Low system flow (air-bound, closed valve, stuck/failed circulator); low pressure or trapped air; clogged/scaled heat exchanger; faulty thermistor. What to do: Check that pressure reads in the normal 17–26 psi band. Overheat usually means a flow problem — call a licensed pro. Don't keep resetting an overheating boiler. |
| E:190 | Electrical grounding fault. Common causes: Boiler not properly grounded; reversed line/neutral at the receptacle; loose/corroded ground; wiring fault. What to do: Not a homeowner repair. Confirm the boiler is on a properly grounded, correctly wired outlet (no extension cords/adapters). Call a licensed pro or electrician. |
| E:430 | High or low water pressure in the heating system. Common causes: Below normal (slow leak, water lost during service); overpressurized (auto-fill too high, waterlogged/failed expansion tank); trapped air or failing pressure sensor; closed valve. What to do: Read the gauge — normal cold range is ~17–26 psi. Adding water or checking the expansion tank should be done by your installer. Repeated low pressure usually means a leak — call a pro. |
| E:443 | Low Water Cut Off (LWCO) activated. Common causes: Insufficient water (significant loss or leak); air-bound system or failed make-up supply; faulty LWCO probe; severely low pressure. What to do: An LWCO trip means the boiler shut down for safety. Don't fire it dry. Check for visible leaks and call a licensed pro to find the cause and refill/bleed correctly. |
| E:540 | High exhaust (flue gas) temperature. Common causes: Heat exchanger fouled with scale or soot; restricted venting; combustion set up wrong / wrong gas type; faulty exhaust thermistor. What to do: A combustion/heat-exchanger issue — not a homeowner repair. Call a licensed pro to inspect the heat exchanger, venting, and combustion. |
| E:610 | Combustion fan fault. Common causes: Failed or seized blower; loose/damaged fan wiring; debris obstructing the fan; board not reading correct fan speed. What to do: One reset is acceptable; if it recurs, call a licensed pro to inspect or replace the blower. Not a homeowner repair. |
| E:720 | Flame rod (flame sensor) fault. Common causes: Dirty/corroded/misaligned flame rod; poor grounding; damaged flame-rod wiring; board fault. What to do: Flame detection is a safety function — needs a tech to clean/inspect or replace the flame rod and verify grounding. Call a licensed pro. |
| E:LC | Scale (lime) build-up in the DHW plate heat exchanger (combi only). Common causes: Hard-water mineral/limescale in the domestic-hot-water heat exchanger; no periodic descaling in a hard-water area; restricted flow from scale. What to do: The fix is a descale/flush, best done professionally; the code clears once flushed. In hard-water areas (much of Utah), schedule annual flushing to protect the heat exchanger and warranty. |
Source: manufacturer documentation
Controls & pumps: Taco, Caleffi, and Grundfos make controls, zone valves, and circulators rather than boilers, so they generally don't show standardized 'fault codes.' Symptoms there (a pump not running, a zone not calling, a relay not switching) are diagnosed by behavior, not a code. Call us and describe what's happening.