BoilerFaultCodesThe 6 most common faults
01
F.22 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
What to try first
Locate the external filling loop, which is usually a silver braided hose underneath the boiler.Open the valves at both ends of the hose to allow water into the system until the pressure gauge reads between 1 bar and 1.5 bar.Close both valves firmly and ensure the hose is disconnected if required by your specific installation.
02
F.00 High Engineer
Your boiler has lost its connection to the sensor that measures how hot the water is inside it, preventing it from heating your home safely.
Full guide for F.0003
F.01 High Engineer
Your boiler has lost its connection to the sensor that monitors the water temperature returning to the unit, causing it to shut down for safety reasons.
Full guide for F.0104
F.10 High Engineer
Your boiler has stopped working because a sensor that monitors water temperature has developed a faulty faulty connection or failed completely, causing the system to shut down for safety.
Full guide for F.1005
F.11 High Engineer
Your boiler has stopped working because a sensor that measures the temperature of water returning to the system is providing an incorrect signal, causing a safety shutdown.
Full guide for F.1106
F.20 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Full guide for F.20on the Vaillant ecoFIT Pure 435
Pressure sensorPressure relief valveExpansion vesselNTC temperature sensorWiring harnessReturn NTC 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