BoilerFaultCodesThe 6 most common faults
Your boiler has shut itself down because it has become too hot inside, likely due to a lack of water flow or a blockage.
Check that your boiler pressure is between 1.0 and 1.5 bar on the display.Ensure all radiator valves and isolation valves are fully open.Press the reset button (indicated by a flame with a line through it) to restart the system.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Locate the silver braided filling loop hoses underneath or near the boilerOpen the one or two small taps on the filling loop until you hear water flowingWatch the pressure gauge and close the taps once the needle reaches between 1 and 1.5 bar
Your boiler has shut down because the water is heating up too quickly or isn't circulating properly between the flow and return pipes.
Check that all radiator valves (TRVs) are fully openEnsure the boiler pressure gauge is between 1.0 and 1.5 barBleed all radiators to remove trapped airReset the boiler using the flame symbol or power button
Your boiler has shut down because it is heating up much faster than it should, which usually means water isn't moving through the system properly.
Check that all radiator valves (TRVs) are turned to the highest settingEnsure the boiler water pressure is between 1.0 and 1.5 barCheck that the external heating bypass valve or isolation valves are fully open
Your boiler has tried to light several times but has been unable to establish a flame, meaning you will have no heating or hot water.
Check if your gas meter has credit (if on a prepayment meter)Verify other gas appliances in your home, like a hob, are working correctlyReset the boiler by pressing the flame/reset button for several seconds
Your boiler was working but has unexpectedly turned itself off because the flame went out and it cannot manage to relight it.
Check that your gas meter has credit and the gas emergency control valve is openInspect the white plastic condensate pipe outside for signs of freezing or blockagesPress the Reset button (indicated by a flame with a line through it) for one second
on the Glow-worm Sustain 12s
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