How much does it cost to fix boiler error code F.78?

Typical repair cost for the boiler F.78 fault is £80-180 including labour.

F.78 High

Boiler Fault Code F.78

Also written as F78 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code F.78 appears across 2 boiler brands and 39 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is confused because it is trying to communicate with an external control box that isn't compatible with its current setup. (As reported on Vaillant ecoTEC)

Pick your boiler brand for the F.78 fix

Glow-worm F.78 6 models Vaillant F.78 33 models

Source

Information for the F.78 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026