F.24 High

Vaillant F.24 Fault Code

Also written as F24 — same fault.

The Vaillant F.24 fault code means: your boiler is overheating too quickly because water isn't flowing through the system correctly, often due to low pressure or trapped air.. It appears on 53 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Safetyswitch-off:Temp.incr.toofast | Pumpblocked,insufficientpumpoutput,airinproduct,systempressure toolow,non-returnvalveblocked/incorrectlyinstalled

What causes the Vaillant F.24 fault?

This fault occurs when the boiler's internal sensors detect that the temperature is rising too rapidly, which usually means heat isn't being carried away from the heat exchanger. The most common reasons are that there isn't enough water pressure to move the heat, air bubbles are trapped in the pump, or the pump itself has seized and stopped circulating water. Basically, the boiler is producing heat faster than the system can distribute it to your radiators.

This issue often appears in autumn when the heating is turned back on for the first time after summer, as internal pump components can seize up during long periods of inactivity.

Typical repair cost £100-£350 (including labour)

DIY fix possible

Check the pressure gauge and top up the water to 1.5 bar if it is too lowBleed any air from your radiators using a radiator keyEnsure all radiator valves and isolation valves are fully open

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Vaillant models that show the F.24 fault code

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

Source

Vaillant F.24 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 27 April 2026