BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the pipe that drains away excess liquid is blocked, likely due to debris or frozen water if it is cold outside.
Why it happens: This fault occurs when the boiler's internal drainage system becomes backed up with liquid that can no longer escape. The most common reason is a blockage in the external pipe, often caused by a buildup of sludge or debris within the condensate trap itself. When the water level rises too high inside the unit, a safety sensor shuts the system down to prevent internal leaking or damage.
Check the white plastic pipe leading outside to see if the end is submerged in water or blocked by debris.If it is freezing weather, gently pour warm (not boiling) water over the external pipe to melt any ice blockages.Ensure any external collection tanks or 'soakaways' are not overflowing or backed up.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Why it happens: This fault occurs when the water pressure inside your heating system drops below a safe level, causing the boiler to shut down to prevent damage. The most common reasons are a slow leak from a pipe or radiator, or a loss of air in the expansion vessel which helps manage pressure changes. If you have recently bled your radiators, this can also cause the pressure to drop enough to trigger this code.
Locate the filling loop (a flexible silver hose) underneath or near the boiler.Slowly open the valves on the filling loop until you hear water flowing.Watch the pressure gauge and close the valves once it reaches 1.5 bar.
Your boiler has failed to ignite, meaning it cannot produce heat for your radiators or hot water.
Why it happens: This fault occurs when the boiler attempts to start up but cannot successfully establish or detect a steady flame. The most common reasons include a lack of gas reaching the burner, a worn-out ignition spark, or a buildup of carbon on the sensor that tells the boiler it is safe to stay lit.
Check if other gas appliances, like a cooker, are working to ensure gas is reaching the property.Ensure your pre-payment gas meter has sufficient credit.Press the 'Reset' button (often marked with a flame symbol) on the boiler control panel.
Your boiler has lost its electrical power supply or experienced a sudden interruption, causing it to shut down safety.
Why it happens: This fault occurs when the boiler’s electronic brain suddenly loses its electrical connection, causing the unit to shut down instantly for safety. It is usually triggered by a blown internal fuse or a failure within the main circuit board that prevents power from flowing through the system. In some cases, an external issue like a tripped circuit breaker or a loose wire in the wall switch can also be the root cause.
Check if there has been a local power cut in your street or homeCheck your property's main fuse box (consumer unit) to see if a circuit breaker has trippedEnsure the boiler’s fused spur switch (usually near the boiler) is turned onTry resetting the boiler by turning the selector knob to the 'Reset' position for 5 seconds
Your boiler has detected that the water is heating up too quickly or not circulating properly through the system, causing a large temperature gap between the pipes.
Why it happens: This fault occurs when the water inside the boiler heats up much faster than it can be moved away, leading to a dangerous heat buildup. The most common reasons are a failed pump that isn't pushing water round or a blockage in the heat exchanger, such as a buildup of sludge or limescale. In some cases, it may simply be that the internal sensors have become faulty and are providing incorrect temperature readings to the control board.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 bar on the pressure gaugeBleed all radiators to remove trapped air that could be blocking water flow
Your boiler is heating up much faster than it should and has shut down to prevent itself from overheating.
Why it happens: This fault occurs when the water inside the boiler gets hot too quickly because it isn't moving away from the heat source fast enough. The most common reasons are a pump that has failed or become stuck, or a blockage within the main heat exchanger that is restricting water flow.
Check if your radiator valves are openEnsure your boiler pressure is between 1.0 and 1.5 barGently bleed your radiators to remove any trapped air
on the Glow-worm EnergySaver Combi
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