BoilerFaultCodesThe 6 most common faults
Your boiler is not receiving the correct electrical power, meaning it cannot start the ignition process to provide heating or hot water.
Why it happens: This fault occurs when the boiler's internal controls detect that the main electrical power is either missing or interrupted before it can reach the ignition system. The most common reason is an external fuse that has blown or a loose connection in the wiring that prevents electricity from flowing correctly through the unit. Without this steady power supply, the boiler cannot safely trigger the spark needed to light the flame.
Check your home's main fuse box or consumer unit to see if a circuit breaker has tripped.Ensure the boiler's isolation switch (usually a fused spur near the boiler) is turned on.Check if other electrical appliances in the house are working to rule out a local power cut.
Your boiler has likely stopped heating because it has reached an unusually high internal temperature and has shut down as a safety precaution.
Why it happens: This fault occurs when the boiler's internal water temperature exceeds a safe limit, triggering a safety sensor to cut the power. It is often caused by a failing pump that isn't circulating water quickly enough or a buildup of sludge and debris blocking the heat exchanger. The system shuts down completely to prevent internal components from melting or warping due to excessive heat.
Wait for the boiler to cool down completely.Locate the overheat reset button on the control panel or underside of the unit.Press the reset button firmly to see if the boiler restarts.
Your boiler appears to have no power reaching it, which is likely caused by an external electrical issue or a blown fuse inside the unit.
Why it happens: This fault occurs when the electrical circuit feeding the boiler is broken, meaning the unit cannot receive the power it needs to operate. The most common reason is a blown fuse within the boiler's internal control board or an issue with the external power switch on the wall. In some cases, a power surge or a failing internal component can cause the fuse to pop as a safety precaution to protect the sensitive electronics.
Check if your home's main fuse board (consumer unit) has tripped and flip the switch back if necessary.Locate the fused spur switch near the boiler (usually a wall switch with a red light) and ensure it is turned on.Check if other appliances in the house are working to rule out a general power cut.
Your boiler has switched itself off because it has reached an unsafe temperature or a safety sensor has detected a fault.
Why it happens: This fault occurs when the water inside the boiler gets too hot, causing a safety switch to trip and shut the system down to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of sludge and scale that blocks the flow through the heat exchanger.
Locate the overheat reset button under the boiler control panelPress the button firmly to reset the tripEnsure all radiator valves are open to allow water to circulate
Your boiler has detected an internal electrical communication error, meaning it cannot safely confirm the fan is working to clear waste gases.
Why it happens: This fault occurs when the boiler's main control board loses electrical contact with the safety sensors that monitor the air flow. The most common reason is a physical break or loose connection in the wiring, or a component failure on the circuit board itself that prevents it from reading the fan's status. Essentially, the boiler's 'brain' can no longer talk to its 'lungs,' so it shuts down for safety.
Full guide for neon3Your boiler is unable to light the pilot flame, which means it cannot fire up to provide heating or hot water.
Why it happens: This fault occurs when the boiler's control system attempts to light the pilot flame but fails to receive the electrical signal or gas flow required to start the ignition process. The most common reason is an electrical failure in the main circuit board or a faulty solenoid preventing the gas valve from opening, meaning the boiler cannot safely begin the heating process.
Full guide for neon4on the Glow-worm Space Saver
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