BoilerFaultCodesThe 6 most common faults
01
F1 High Engineer
Your boiler is trying to start up but is failing to light the burner, which means you currently have no heating or hot water.
Full guide for F102
F4 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage or safety risks.
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 safety issues.
Full guide for F504
F6 High Engineer
Your boiler's temperature sensor is failing to provide a reading, so the system has shut down to prevent overheating.
Full guide for F605
F7 High Engineer
Your boiler is struggling to detect the temperature of your hot water supply, so it has safely shut down to prevent overheating.
Full guide for F706
F9 High Engineer
Your boiler is struggling to accurately detect the water pressure inside the system, which is preventing it from firing up safely.
Full guide for F9on the Saunier Duval Enviroplus
Ignition electrodeIgnition leadGas valvePrinted circuit board (PCB)NTC SensorPrimary Heat Exchanger
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 Saunier Duval 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