BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because it has either become too hot or the water pressure in the system has dropped too low.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature or there isn't enough water circulating to carry heat away from the burner. The most common reasons are a build-up of air or debris blocking the pipes, a failing pump that can no longer move the water, or a simple drop in system pressure due to a leak.
Check the pressure gauge on your system and top up to 1.5 bar if it is lowEnsure all radiator valves and boiler isolation valves are fully openPress the reset button on the control panel once the unit has cooled down
Your boiler is attempting to start but cannot successfully light or detect a steady flame, so it has shut down for safety.
Why it happens: This fault occurs when the boiler cannot establish a stable flame to begin the heating process after several attempts. It is usually caused by a blocked pilot light injector, a faulty electronic ignition component, or a gas valve that is failing to release gas to the burner.
Check that your gas emergency control valve is open and other gas appliances are working.Press the reset button on the front control panel.Ensure your decorative fireplace or external flue is not blocked by debris or ice.
Your boiler has detected an electrical supply issue, likely caused by a tripped switch, a blown fuse, or a temporary power failure.
Why it happens: This fault occurs when the boiler's control system detects an interruption or an irregularity in the electrical current reaching the unit. It is most commonly caused by a blown 3-amp fuse in the external spur switch or a failure within the boiler's internal circuit board which prevents it from processing power correctly.
Check your home's main fuse box (consumer unit) to see if any circuit breakers have tripped.Inspect the fused spur switch near the boiler and replace the 3-amp fuse if it has blown.Turn the boiler power switch off and back on to attempt a reset of the internal electronics.
Your boiler has detected that the water pressure is too low to operate safely, causing it to lock out.
Why it happens: This fault occurs when the internal sensors detect that there isn't enough water pressure inside the system to safely heat your home. The most common reason is a slow leak in the pipework or radiators, though it can also happen if the system was recently drained and not refilled correctly. Without sufficient water, the boiler shuts down to prevent the internal components from overheating and sustaining permanent damage.
Check the water pressure gauge on your system.If the pressure is below 1.0 bar, use the external filling loop to top up the system to 1.5 bar.Reset the boiler to see if the light clears.
Your boiler is not receiving electrical power or has an internal blown fuse, meaning it cannot start the ignition process.
Why it happens: This fault occurs when the electrical circuit required to wake up the boiler is broken, preventing the control board from receiving power. The most common reason is a blown fuse within the boiler or at the wall switch, often caused by a sudden electrical surge or a faulty internal component like a failing pump or fan. If the fuses are intact, it typically indicates that the main printed circuit board has suffered an electrical failure and can no longer process commands.
Check if your home's main electrical consumer unit has a tripped circuit breakerEnsure the boiler's external switch or fused spur is turned onChange the fuse (usually 3A) in the external wall switch/spur
Your boiler has switched itself off because it has reached an unsafe temperature or it has detected a faulty component in its safety system.
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 debris that blocks the flow, but it can also be caused by a sensor that has simply become faulty over time.
Wait for the boiler to cool down completely (at least 20-30 minutes).Locate the manual reset button, which is usually found under the boiler casing.Press the reset button once; if the neon light comes back on and stays on, the system has reset.
on the Glow-worm Ultimate3
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