Overview
F.29 on a Vaillant Turbomax Plus 824/828E means the boiler detected a flame failure after it had lit — in other words the burner ignited at some point but the flame went out during operation and the boiler has entered lockout for safety. The boiler shuts down to prevent unburned gas building up, so this is a safety response rather than a normal operating condition. There are multiple causes: a frozen or blocked condensate pipe (common in cold weather), interrupted or low gas supply, a faulty gas valve, flue blockage or wind-induced flue disturbance, ignition/electrode failure, burner contamination, internal leak affecting electronics, or failed control electronics. Severity ranges from minor (frozen condensate pipe that you can safely thaw) to serious (gas-supply or flue faults, internal leaks or failed gas valve) that require a Gas Safe registered engineer. Simple checks and a reset can sometimes restore operation, but any work on gas components, the flue or internal boiler parts must be left to a qualified professional.
Possible Cause: Flame extinguished
Troubleshooting Steps
Safety precautions:
- If you smell gas or suspect a leak: do not operate switches or the boiler. Turn off the gas at the meter, evacuate the property, and call the gas emergency number immediately.
- Only a Gas Safe registered engineer should work on gas valves, burners, electrodes, the flue, or any internal boiler parts. Do not attempt internal repairs if you are not qualified.
- If you are waiting for an engineer, isolate the boiler gas supply at the external isolation valve if you know how and it is safe to do so.
Initial checks a homeowner can do (safe, non-invasive):
1. Check other gas appliances (hob, oven) to confirm the property has gas supply. If nothing else works, contact your gas supplier.
2. If you have a prepayment meter, check it has credit and that the meter is not locked or indicating a fault.
3. Check the boiler display for F.29 and note any additional fault codes or history — take a photo for the engineer.
4. Check the boiler power and water pressure: ensure the boiler has mains power and system pressure is within the normal range shown on the pressure gauge (consult your manual for required pressure). This won’t usually cause F.29 but is worth confirming.
5. Check the flue terminal on the outside of the house for obvious obstructions (nests, leaves, debris) and that the flue guard isn’t blocked. Do this visually from ground level only — do not climb or use tools on the roof yourself.
6. Listen for gurgling noises around the boiler which can indicate a blocked condensate path.
Reset procedure (safe to try):
1. Try a boiler reset following the instructions in your user manual. Switch the boiler off at the mains or boiler switch, wait 30 seconds, switch it back on and press the reset button once. Some boilers will allow one reset attempt; if the fault returns immediately or after one reset, do not keep resetting repeatedly — this can hide a persistent safety issue.
2. If the fault clears and the boiler runs, monitor it for a while to ensure it stays lit and no other codes appear. If it reappears, book an engineer.
If you suspect a frozen/blocked condensate pipe (common in cold weather):
1. Locate the condensate pipe (usually a small plastic pipe running outside to a soil/drain). If it is icy or you hear gurgling, it may be frozen or blocked.
2. Carefully pour warm (not boiling) water along the length of the exposed condensate pipe to thaw it, or wrap a warm cloth and pour warm water. Do not use a blowtorch, boiling water or any aggressive methods. Insulate the pipe afterwards to reduce re-freezing.
3. After thawing, reset the boiler as above. If the boiler still shows F.29, call an engineer.
Other diagnostics and fixes that should be carried out by a Gas Safe engineer:
- Check gas supply pressure at the appliance and confirm the gas isolation valve and meter are correct and working. Low or interrupted gas supply requires supplier involvement or valve replacement by an engineer.
- Inspect and test the gas valve and gas train for leaks, correct operation and proper gas flow.
- Clean and inspect the burner for debris or damage; replace if required.
- Check ignition electrode and leads for wear or damage; replace or re-gap as needed.
- Inspect flue system for blocked, displaced or damaged sections and for signs of flue gas backflow; repair or replace as required.
- Inspect for internal water leaks that could have damaged ignition leads or the PCB and replace faulty components.
- Test and, if necessary, replace control electronics (PCB) if they are failing to manage gas valve/ignition correctly.
When to call a professional now:
- If a reset does not clear the fault or the F.29 returns.
- If you cannot confirm the gas supply is present and working via other appliances or the meter.
- If you find a blocked/iced condensate pipe that you cannot safely clear, or if clearing does not fix the fault.
- If you suspect flue blockage, gas valve, burner, electrode or internal leak issues.
Final notes:
- F.29 is a safety lockout triggered by flame loss — it should be treated seriously. Simple steps (check gas supply, reset once, thaw condensate) can sometimes restore the boiler, but anything involving the gas system, flue, burner or internal components must be done by a Gas Safe registered engineer. Record the fault code and any conditions (cold weather, gurgling, smell of gas, other appliance failures) and give that information to the engineer to speed diagnosis.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Vaillant Turbomax Plus 824/828E.