BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because it has either become 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 temperature or there isn't enough water circulating to carry heat away from the burner. The most common reasons are a build-up of air or debris blocking the pipes, a failing pump that can no longer move the water, or a simple drop in system pressure due to a leak.
Check the pressure gauge on your system and top up to 1.5 bar if it is lowEnsure all radiator valves and boiler isolation valves are fully openPress the reset button on the control panel once the unit has cooled down
Your boiler is attempting to start but cannot successfully light or detect a steady flame, so it has shut down for safety.
Why it happens: This fault occurs when the boiler cannot establish a stable flame to begin the heating process after several attempts. It is usually caused by a blocked pilot light injector, a faulty electronic ignition component, or a gas valve that is failing to release gas to the burner.
Check that your gas emergency control valve is open and other gas appliances are working.Press the reset button on the front control panel.Ensure your decorative fireplace or external flue is not blocked by debris or ice.
Your boiler has detected an electrical supply issue, likely caused by a tripped switch, a blown fuse, or a temporary power failure.
Why it happens: This fault occurs when the boiler's control system detects an interruption or an irregularity in the electrical current reaching the unit. It is most commonly caused by a blown 3-amp fuse in the external spur switch or a failure within the boiler's internal circuit board which prevents it from processing power correctly.
Check your home's main fuse box (consumer unit) to see if any circuit breakers have tripped.Inspect the fused spur switch near the boiler and replace the 3-amp fuse if it has blown.Turn the boiler power switch off and back on to attempt a reset of the internal electronics.
Your boiler has lost power because of an electrical issue or a blown fuse inside the control unit.
Why it happens: This fault occurs when the boiler's internal computer loses electrical power, preventing the system from starting up at all. The most common reason is a blown fuse on the circuit board, which often happens due to an unexpected power surge or a failing internal component causing an electrical short.
Full guide for Neon1Your boiler has stopped working because it cannot safely confirm that the fan is clearing exhaust gases from the system.
Why it happens: This fault occurs when the boiler's internal computer tries to start the fan but cannot confirm that a safe flow of air is moving through the system. The most common cause is either a mechanical failure of the fan itself or a blockage in the small plastic tubes that connect to the air pressure sensor, preventing the boiler from knowing it is safe to ignite.
Full guide for Neon3Your boiler has detected an internal electrical communication fault which is preventing it from starting up safely.
Why it happens: This fault occurs when the boiler's main control board loses the ability to communicate with the sensors that monitor air flow and safety. The most common reason is a failure of the internal electrical circuits on the main control board or a loose connection in the wiring that links it to the air pressure switch. Because the boiler cannot confirm it is safe to vent exhaust gases, it prevents the burner from firing as a safety precaution.
Full guide for Neon 3 liton the Glow-worm Ultimate
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