BoilerFaultCodesThe 6 most common 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 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 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 stopped working because the fan isn't starting up to safely clear waste gases from the system.
Why it happens: This fault occurs when the boiler's safety system detects that the fan isn't spinning fast enough to move exhaust gases out of the flue. It is often caused by a mechanical failure in the fan motor itself or a blockage in the small plastic tubes that connect to the air pressure switch. Without the fan functioning correctly, the boiler cannot safely light the flame and will shut down as a precaution.
Full guide for 02on the Glow-worm 30ci Plus
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