BoilerFaultCodesThe 4 most common faults
Your boiler is not receiving power, which means it cannot turn on to provide heating or hot water.
Why it happens: This fault occurs when the boiler's control system is completely deprived of electrical power, often due to a blown internal fuse or a failure within the main circuit board. The most common reason is an electrical surge or a faulty internal component causing a short circuit, which trips the protection to prevent further damage.
Check if the boiler's fused spur switch is turned onCheck your home's main consumer unit (fuse box) to see if a circuit breaker has trippedReplace the 3-amp fuse in the boiler's external wall switch
Your boiler has stopped running because it has either detected that it is getting too hot or the water pressure in the system has dropped too low.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe operating temperature or if there isn't enough water circulating to carry heat away. The most common reasons are a build-up of sludge blocking the heat exchanger, a failing pump, or a simple loss of pressure in the central heating pipes.
Check the pressure gauge on your system and top it up to 1.5 bar using the filling loop if it is low.Ensure all radiator valves and boiler isolation valves are fully open to allow water flow.Wait for the unit to cool down and check if there is a manual reset button on the bottom or front of the casing.
Your boiler is trying to start up but cannot light the small pilot flame needed to ignite the main heating system.
Why it happens: This fault occurs when the boiler's internal safety system fails to detect a constant flame after several attempts to spark. The most common reasons are a blocked pilot jet preventing gas flow, a worn-out ignition lead that can no longer create a spark, or a faulty sensor that cannot confirm the flame is actually lit.
Check that your gas emergency control valve is in the 'on' positionVerify that other gas appliances in your home, such as a hob, are working correctlyPress the reset button on the front control panel to attempt a restart
Your boiler has stopped working because it cannot confirm that the internal fan is safely clearing waste gases out of the flue.
Why it happens: This fault occurs when the boiler's safety system detects that the fan isn't spinning fast enough or the air pressure is incorrect to safely push exhaust fumes outside. The most common reasons are a seized fan motor, a perished rubber tube leading to the sensor, or a blockage within the flue pipe itself.
Full guide for Neon 3 NOT liton the Glow-worm Glow-worm Micron 100FF 120FF
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 Glow-worm 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