BoilerFaultCodesThe 5 most common faults
01
F0 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 silver flexible hose) underneath or near the boiler.Slowly open the tap or taps on the filling loop until you hear water flowing.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps fully.
02
F1 High DIY-safe
Your boiler has failed to light or has lost its flame, so it has shut down for safety purposes.
What to try first
Check if your gas meter has credit and the gas supply to the house is turned onCheck if other gas appliances in your home, like a hob, are working correctlyPress the reset button on the front of the boiler to try and restart it
03
F2 High Engineer
Your boiler has stopped working because it cannot correctly measure the temperature of the water inside the pipes.
Full guide for F204
F3 High Engineer
Your boiler is unable to circulate water properly through its internal heating system, causing it to shut down for safety.
Full guide for F305
F4 Medium Engineer
Your boiler is struggling to accurately measure the temperature of your hot water, which usually means your taps will only run cold.
Full guide for F4on the Protherm 100EC
Filling loop valvePressure sensorExpansion vesselIgnition electrodeGas valvePCB (Printed Circuit Board)
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 Protherm 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