BoilerFaultCodes
The most common Glow-worm faults
Your boiler has stopped working because it cannot light the gas burner to provide heating or hot water, usually because the gas supply is interrupted or the ignition spark has failed.
Why it happens: This fault occurs when the boiler attempts to light but fails to detect a flame after several tries, forcing the system into a safety shutdown. The most common reasons are an interruption in the gas supply, a build-up of carbon on the ignition probes, or a component failure that prevents the spark from starting the fire.
Check if your gas meter has credit or if other gas appliances in your home are working.Ensure the blue gas isolation valve under the boiler is in the 'open' position (aligned with the pipe).Press the 'Reset' button (indicated by a flame with a line through it) and hold for one second.
Your boiler has stopped working because it cannot light the gas needed to provide heating and hot water.
Why it happens: This fault occurs when the boiler attempts to start up but fails to sense a flame after several attempts. The most common reasons are a lack of gas reaching the unit, a dirty ignition electrode that can no longer spark, or a faulty gas valve failing to open.
Check if your gas supply is turned on at the meterCheck if other gas appliances, like a hob, are working correctlyPress the reset button (indicated by a flame with a line through it) for five seconds
Your boiler has shut down because it has detected it is getting too hot, usually due to a lack of water flow or a circulation blockage.
Why it happens: This fault occurs because the internal sensors have detected the water inside the boiler is reaching a dangerously high temperature, triggering an automatic shutdown to prevent damage. The most common reason is that the water isn't moving through the system quickly enough, often due to a failed pump, a blockage in the pipework, or a build-up of sludge in the heat exchanger.
Check if your radiator valves are open to ensure water can circulate.Check the boiler pressure gauge and top it up to 1.5 bar if it is low.Gently press the reset button on the front of the boiler.
Your boiler's main control screens are having trouble talking to each other, which means the boiler doesn't know what settings you are asking for.
Why it happens: This fault occurs when the communication link between the boiler's internal computer and the front display panel is broken. It is usually caused by a loose connection cable or internal electrical wear on one of the circuit boards, which prevents your instructions from reaching the burner.
Turn off the electrical power supply to the boiler at the fused spur switch.Wait approximately 60 seconds for the electronics to fully discharge.Turn the power back on to see if the communication link resets.
Your boiler has reached an unsafe temperature and has shut itself down to prevent damage or overheating.
Why it happens: This fault occurs when the water inside the boiler gets too hot, causing a safety sensor to trip and shut the system down. The most common reasons are a pump that has stopped moving water around the system or a build-up of sludge and debris that is blocking the internal pipework.
Check that all radiator valves are fully open to allow water to circulate.Ensure the boiler pressure gauge is between 1.0 and 1.5 bar.Reset the boiler using the power button or reset switch and see if the fault clears.
Your boiler is having trouble sending signals between its internal electrical parts, which is preventing it from working correctly.
Why it happens: This fault occurs when the 'brain' of the boiler loses contact with its internal electrical components, meaning it can no longer send or receive instructions. It is usually caused by a loose connection in the wiring or a hardware failure within the main control board itself. Occasionally, outside electrical interference from other household appliances can disrupt these signals and trigger the error.
Turn the boiler off at the fused spur switchWait 60 secondsTurn the power back on and press the 'Reset' button
Your boiler has lost water pressure and has shut down to prevent damage, meaning you currently have no heating or hot water.
Why it happens: This fault occurs when the water pressure inside your heating system drops below a safe operating level, causing the boiler to shut down to protect the internal components. The most common reasons are a small leak somewhere in your pipework or radiators, or the pressure being manually drained during recent maintenance without being refilled.
Locate the filling loop (usually two blue or black levers) underneath the boiler.Slowly open both levers until you hear water flowing and the pressure gauge rises.Close both levers tightly once the gauge reaches 1.5 bar.
Your boiler has too much water inside it, causing the internal pressure to rise to an unsafe level.
Why it happens: This fault occurs when the water pressure inside your heating system exceeds a safe operating limit, often because the filling loop valve has been left slightly open or is leaking water into the system. It can also happen if the expansion vessel, which manages pressure changes as water heats up, has failed or lost its air charge. In some cases, a faulty plate heat exchanger may be allowing high-pressure mains water to leak internally into the heating circuit.
Check that the filling loop valves are fully closed and not leakingBleed water from a radiator using a radiator key to reduce the system pressureMonitor the pressure gauge until it returns to between 1.0 and 1.5 barIf pressure continues to rise on its own, turn off the water mains and call an engineer
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