BoilerFaultCodesThe 6 most common faults
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 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 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
Your boiler is failing to start because it cannot confirm that the internal fan is effectively clearing exhaust gases, which prevents it from igniting safely.
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.
Full guide for 0 8Your boiler detects a flame when it shouldn't, which is causing it to shut down for safety.
Why it happens: This fault occurs when the boiler's internal sensor incorrectly detects a flame after the burner has been told to switch off. This is most commonly caused by a carbon-coated or damaged sensing probe sending a false electrical signal, or a moisture-damaged control board misreading the system's status.
Full guide for 30Your boiler's internal computer has encountered a critical error and can no longer control the heating and hot water functions safely.
Why it happens: This fault occurs when the boiler's main control board experiences a hardware failure or a memory error, meaning it can no longer process data correctly. The most common reason is natural wear and tear of the electronic components, though electrical surges or moisture getting onto the board can also trigger this complete failure.
Full guide for 06on 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