BoilerFaultCodesThe 6 most common faults
Your boiler has lost power or has insufficient water pressure to operate safely, meaning it cannot provide heating or hot water until reset.
Why it happens: This fault occurs when the boiler's internal computer stops receiving a steady flow of electricity or detects that the system doesn't have enough water to function. The most common reason is a simple drop in water pressure, but it can also be triggered by a blown internal fuse or a failing main circuit board. Because the boiler cannot guarantee it will run safely under these conditions, it shuts down entirely as a protective measure.
Check the pressure gauge on the front of the boiler or in your airing cupboard; if below 1.0 bar, top it up using the filling loopCheck your home's consumer unit (fuse box) to ensure the heating circuit hasn't trippedSwitch the boiler off at the wall, wait 30 seconds, and switch it back on to reset the electronics
Your boiler has switched itself off because it has become too hot internally, likely due to a circulation problem or a faulty safety sensor.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature, triggering a safety switch to shut the system down to prevent damage. The most common reasons are a pump failure preventing heat from leaving the boiler or a blockage in the system restricting water flow. It can also be caused by a faulty internal sensor that is incorrectly detecting a high temperature.
Check that your pump is running and not stuckEnsure all radiator valves are open to allow water flowOnce the unit has cooled, press the reset button located on the overheat thermostat (refer to manual for exact location)
Your boiler has stopped working because the water pressure in the central heating system is too low.
Why it happens: This fault occurs when the water level inside your central heating system drops too low for the boiler to operate safely. It is usually caused by a small leak in the pipework or radiators, or because the air cushion inside the expansion vessel has depleted over time.
Locate the filling loop, which is usually a silver flexible hose with one or two small taps.Slowly open the tap(s) until you hear water entering the system.Watch the pressure gauge and close the taps firmly once it reaches between 1.0 and 1.5 bar.
Your boiler has stopped working because the water pressure in the central heating system is too low.
Why it happens: This fault occurs when there isn't enough water circulating in your central heating system to operate safely. The most common reasons are a slow leak from a radiator valve or pipework, or simply that the system needs topping up after you have bled air from your radiators.
Locate the external filling loop, which is usually a silver flexible hose with two small valves.Open both tap handles slowly until you hear water flowing into the system.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close both taps tightly.The red light should extinguish and the boiler should restart automatically.
Your boiler has detected an issue with the ventilation system, meaning it cannot safely clear waste gases and has shut down as a precaution.
Why it happens: This fault occurs when the boiler's internal safety system can no longer confirm that the fan is successfully pushing harmful exhaust gases out of the flue. The most common reason is that the fan has failed, the air pressure sensor has malfunctioning electrical contacts, or the small tubes connecting them have become blocked with dust or debris.
Full guide for Neon3Your boiler is attempting to start but cannot light or maintain the flame needed to provide heating and hot water.
Why it happens: This fault occurs when the boiler's internal safety system fails to detect a steady flame after several attempts to light. The most common reasons are a blocked pilot light burner or a worn-out sensor that can no longer tell the control board that the gas has successfully ignited.
Full guide for Neon4on the Glow-worm Fuelsaver Complheat 40 55
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