Vaillant is one of the most widely installed boiler brands in the UK. This page collects our guides and the common Vaillant combi boiler fault codes, with what each one means and what you can safely check yourself.
Vaillant combi boiler error codes
- F.0 Flow temperature sensor interrupted
- F.1 Return temperature sensor interrupted
- F.10 Flow temperature sensor short-circuited
- F.11 Return temperature sensor short-circuited
- F.12 Hot water temperature sensor short-circuited
- F.20 Safety thermal cut-out has operated
- F.22 Low water pressure in the system
- F.23 Temperature difference between flow and return too great
- F.24 Temperature rising too quickly
- F.25 Flue gas temperature too high
- F.27 Flame signal detected while the burner is off
- F.28 No flame detected during ignition
- F.29 Re-ignition after flame loss was unsuccessful
- F.32 Fan fault
- F.35 Air/flue pipe blocked
- F.52 Mass flow sensor fault
- F.53 Combustion regulation fault
- F.54 Fault in the gas supply
- F.57 Boiler not burning correctly in comfort mode
- F.62 Flame switch-off detected after a delay
- F.70 Device specific number (DSN) incorrect or missing
- F.72 Invalid temperature difference between flow and return sensors
- F.75 Pressure change too low when the pump starts
- F.83 Little or no temperature rise when the burner starts
- F.84 Flow and return sensor readings are implausible
- F.88 Electrical connection to the gas valve interrupted
Should you repair or replace?
As a rough rule, if your boiler is more than 10–12 years old and the repair is over a few hundred pounds, it's worth getting a replacement price before you commit. Parts for older models also get harder to find.
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