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 is not receiving electrical power or has shut down because there is not enough water pressure in the system.
Why it happens: This fault occurs when the boiler's internal computer loses electrical power or detects that the water level has dropped too low to operate safely. It is often caused by a simple blown fuse on the control board or a leak in the system that has drained the pressure. Without this power or water pressure, the boiler shuts down completely to prevent any internal damage.
Check that the boiler's main power switch is turned on.Check your home's consumer unit (fuse box) to see if a circuit has tripped.Check the pressure gauge and, if below 1 bar, use the filling loop to top up the water pressure.
Your boiler has shut itself down because it became too hot, likely due to a circulation problem or a component failure.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to shut the system down to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of debris in the pipes that blocks flow. In some cases, the sensor itself may have failed and is incorrectly reporting that the boiler is overheating.
Locate the manual reset button on the overheat thermostat (usually behind the front panel or at the bottom).Press the button to reset the boiler once the unit has cooled down.Ensure all radiator valves are open and your heating system pump is running.
on 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