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 or there is trapped air.
What to try first
Locate the filling loop valves underneath your boiler.Open the valves slowly to let water in until the pressure gauge reads between 1 and 1.5 bar.Close the valves tightly and restart your boiler.
02
F1 High Engineer
Your boiler has safely shut itself down because it failed to ignite, meaning you currently have no heating or hot water.
Full guide for F103
F2 High Engineer
Your boiler has temporarily stopped working because the water temperature inside the system has dropped too low or a sensor has stopped reading it correctly.
Full guide for F204
F3 High Engineer
Your boiler has stopped working because scale or debris has built up and blocked the internal heat exchanger.
Full guide for F305
F4 Medium Engineer
Your boiler is struggling to accurately measure your hot water temperature, which usually means it will temporarily stop providing hot water until the sensor is fixed.
Full guide for F4on the Protherm 100EC
Water pressure sensorExpansion vesselIgnition electrodeGas valvePrinted Circuit Board (PCB)Central heating temperature sensor (NTC thermistor)
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