BoilerFaultCodesThe 6 most common faults
01
F1 High Engineer
Your boiler is trying to start up but cannot successfully light the flame, so it has stopped working for your safety.
Full guide for F102
F4 High Engineer
Your boiler is trying to start up but is failing to stay lit, so it has turned itself off for safety.
Full guide for F403
F5 High Engineer
Your boiler has detected that it is getting too hot and has automatically shut itself down to prevent any damage or danger.
Full guide for F504
F6 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the water circulating through your heating system, so it has safely shut down to prevent overheating.
Full guide for F605
F10 High Engineer
Your boiler is unable to read the temperature of the water returning from your radiators, so it has shut down to prevent overheating.
Full guide for F1006
F11 High Engineer
Your boiler's computer has lost the ability to communicate with its internal control sensors, so it has shut down as a precaution.
Full guide for F11on the Vaillant ecoMAX Pro 18E
Ignition electrodeGas valveCircuit board (PCB)Printed Circuit Board (PCB)Flame sensorPump
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