BoilerFaultCodesThe 5 most common faults
01
A1 High DIY-safe
Your boiler has detected that it is running without enough water inside, which is often caused by a leak or a pump that has jammed or failed.
What to try first
Check the pressure gauge on the boiler and top it up to 1.5 bar using the filling loopInspect visible pipework and radiators for any signs of water leaksReset the boiler to see if the error clears after repressurising
02
A8 High Engineer
Your boiler has lost its connection to your external room thermostat or heating controls, meaning it doesn't know when to turn on or off.
Full guide for A803
F1 High Engineer
Your boiler has stopped working because an internal safety fuse has failed, cutting off power to the system's control board.
Full guide for F104
F2 High Engineer
Your boiler has stopped working because an internal electrical fuse has blown, cutting off the power needed for it to operate.
Full guide for F205
265 Low DIY-safe
Your boiler is temporarily limiting its power output because it is producing more heat than your radiators or taps can currently take away.
What to try first
Ensure all radiator valves (TRVs) are fully open to allow heat to circulate.Check that the boiler pressure is between 1 and 1.5 bar on the pressure gauge.Deep-clean any magnetic system filters if you are familiar with the process.
on the Worcester Bosch Junior 28i
Central heating pumpPump capacitorAutomatic air ventRF ReceiverInternal Wiring HarnessExternal Room Thermostat
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 Worcester Bosch 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