How much does it cost to fix Vaillant error code F.29?

Typical repair cost for the Vaillant F.29 fault is £100-350 including labour.

F.29 High

Vaillant F.29 Fault Code

Q: What does the Vaillant F.29 fault code mean?

Your boiler has lost its flame while running and cannot manage to restart itself, likely due to a temporary interruption in the gas supply or a component failure.

Also written as F29 — same fault.

The Vaillant F.29 fault code means: your boiler has lost its flame while running and cannot manage to restart itself, likely due to a temporary interruption in the gas supply or a component failure.. It appears on 46 Vaillant models in our database.

Technical description: Flame goes off during operation and subsequent ignition attempts failed: Gas supply temporarily stopped, ignition transformer has spark failure, faulty earthing of appliance

What causes the Vaillant F.29 fault?

This fault occurs when the boiler’s flame is lost while it is already running, rather than failing to start initially. It is usually caused by a temporary drop in gas pressure, a build-up of debris on the ignition components, or an electrical fault that prevents the boiler from detecting its own flame. When the system can no longer confirm a stable flame is present, it shuts down as a safety precaution.

This fault is more common during extreme cold spells, as freezing temperatures can lead to blocked condensate pipes or external gas meter issues that restrict gas flow.

Typical repair cost £100-350 (including labour)

DIY fix possible

Check if other gas appliances, like a hob, are working to ensure gas is reaching the property.If you have a pre-payment meter, check that you have sufficient credit.Press the reset button (indicated by a flame symbol with a cross) for one second to see if the boiler restarts.

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Vaillant models that show the F.29 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant F.29 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026