BoilerFaultCodesThe 6 most common faults
01
F1 High Engineer
Your boiler has automatically shut down for safety because it detected that the internal water temperature has become dangerously high.
Full guide for F102
F2 High Engineer
Your boiler is struggling to accurately measure the temperature of your hot water supply, so it has stopped heating water to prevent overheating.
Full guide for F203
F3 High Engineer
Your boiler has stopped working because it is unable to accurately measure the temperature of the water inside the system.
Full guide for F304
F4 High Engineer
Your boiler has failed to start because it cannot detect a flame or drain water properly, so it has safely shut itself down to prevent any issues.
Full guide for F405
F8 High Engineer
Your boiler has detected that the air circulation system is not operating at the correct speed, so it has safely shut itself down to prevent unsafe operation.
Full guide for F806
F9 High Engineer
Your boiler has detected that the internal exhaust fan is spinning when it should be turned off, which is a safety fault that prevents the boiler from starting up.
Full guide for F9on the Heatline Sargon 30
Overheat thermostatCentral heating pumpPCBDomestic Hot Water (DHW) NTC ThermistorWiring harnessNTC Temperature Sensor
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 Heatline 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