BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has stopped working because the amount of water circulating inside the system has dropped too low to operate safely.
What to try first
Locate the external filling loop, which is usually a small silver braided hose with one or two valves under your boiler.Open the valve(s) slowly to allow mains water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.Close the valve(s) tightly and restart the boiler.
02
F.00 High Engineer
Your boiler has lost its connection to the temperature sensor, meaning it no longer knows how hot the water is and has stopped working to keep you safe.
Full guide for F.0003
F.01 High Engineer
Your boiler has lost the connection to the sensor that monitors the temperature of the water returning to the unit, causing it to stop working for safety reasons.
Full guide for F.0104
F.10 High Engineer
Your boiler has stopped working because a sensor that measures water temperature is providing an incorrect signal, so the system has safely shut down to prevent overheating.
Full guide for F.1005
F.11 High Engineer
Your boiler has detected a faulty signal from a heat sensor, causing it to shut down for safety to prevent overheating.
Full guide for F.1106
F.20 High Engineer
Your boiler has detected that it is getting too hot and has automatically shut itself down to prevent damage.
Full guide for F.20on the Vaillant ecoFIT Pure 825
Pressure sensorPressure relief valveExpansion vesselFlow temperature sensor (NTC)Wiring harnessReturn temperature sensor
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Vaillant shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue