BoilerFaultCodesThe 6 most common faults
01
F22 High DIY-safe
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
What to try first
Locate the filling loop (usually a flexible silver hose) underneath the boiler.Open the valves on the filling loop to allow cold mains water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (usually 1.0 to 1.5 bar).Close the valves tightly and turn the boiler off and on again to clear the fault.
02
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 F103
F2 High Engineer
Your boiler is struggling to clear exhaust gases properly, so it has safely shut itself down to prevent any risk.
Full guide for F204
F3 High Engineer
Your boiler is having trouble managing the air it needs to burn gas safely, so it has shut itself down to prevent any issues.
Full guide for F305
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 F406
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 F5on the Saunier Duval Enviroplus
Pressure relief valveExpansion vesselPressure sensorIgnition electrodeIgnition leadGas valve
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