Occurs if flame is detected when there should be no flame
The FLAME FAULT error code on Weil-Mclain boilers indicates occurs if flame is detected when there should be no flame.
Weil-Mclain FLAME FAULT means: occurs if flame is detected when there should be no flame. On this component the documented failure modes are no gas reaching the burner, or the gas supply is shut off, ignition or detection electrode dirty, worn or out of position or flue or air intake blocked or restricted. You can safely reset the boiler once — if FLAME FAULT returns, do not keep resetting. A qualified heating engineer should diagnose the root cause.
What Does FLAME FAULT Mean
The FLAME FAULT code is shown by the boiler’s control board when it detects occurs if flame is detected when there should be no flame. The boiler then stops instead of continuing to run in that condition: the code is the appliance reporting a problem, not proof that the boiler is broken.
| What you see on the boiler |
|---|
| The display shows FLAME FAULT and the boiler stops until the fault is cleared |
Common Causes
The manufacturer does not publish a cause list for this specific code. The causes below are the failure modes documented for the same component on other boilers, confirmed by the service literature of 11 different manufacturers.
| Cause |
|---|
| No gas reaching the burner, or the gas supply is shut off |
| Ignition or detection electrode dirty, worn or out of position |
| Flue or air intake blocked or restricted |
| Mains gas pressure too low |
| Faulty gas valve, or its wiring and connector |
Safety Warning
FLAME FAULT involves electrical or pressure-related components. Do not attempt repairs without proper qualifications. Ensure the boiler is electrically isolated before any inspection. If you notice water leaks, unusual sounds, or pressure anomalies, contact a qualified heating engineer immediately.
Parts & Prices
Prices shown are indicative. Actual prices and availability vary by region.
How to Fix It
Burner may be operating too hot due to incorrect combustion. Inspect flame and conduct combustion test. Force boiler into high fire. Check flue gases with combustion analyzer and correct using the maintenance and startup procedure in this manual
Verify FLAME SIGNAL value quickly goes to zero on the DIAGNOSTICS - INPUTS screen when the gas valve closes
Check for flame at burner via flame current with burner off. Turn boiler off and watch flame through observation port. If flame continues after shut down replace gas valve
Check that the gas service valve is open and that other gas appliances in the property work. If they do not, the problem is the gas supply, not the boiler.
Inspect the ignition and detection electrode: clean off any deposits, check the gap and position against the manual, and replace it if it is worn.
Inspect the flue and air intake along their whole length, including the outside terminal, and clear any obstruction or debris.
Refer to the Weil-Mclain service documentation for the detailed procedure. Only a qualified engineer should carry out these repairs.
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Affected Models
Weil-Mclain models that can display fault code FLAME FAULT:
| Model Family | Output Range | Frequency |
|---|---|---|
| All Weil-Mclain models | — | Possible |
Frequently Asked Questions
Burner may be operating too hot due to incorrect combustion. Inspect flame and conduct combustion test. Force boiler into high fire. Check flue gases with combustion analyzer and correct using the maintenance and startup procedure in this manual. According to the technical documentation, this is the first check on the list for FLAME FAULT.
FLAME FAULT is not classified as a high-severity fault, so the boiler can be reset once. If FLAME FAULT comes back, stop resetting: the underlying cause is still there and needs a qualified heating engineer.