BoilerFaultCodesThe 6 most common faults
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.
Your boiler has lost electrical power, which is usually caused by an issue with the mains supply or a blown internal fuse.
Why it happens: This fault occurs when the boiler is not receiving the electrical power it needs to operate, causing the control panel to go dark except for the error light. The most common reason is a blown fuse on the main circuit board or a tripped switch in your home's fuse box, often triggered by a sudden power surge or a failing internal component. In some cases, it can simply be that the external power switch for the boiler has been accidentally turned off.
Check if other appliances in the house are working to rule out a general power cutEnsure the boiler's fused spur switch (usually near the boiler) is turned onCheck your home's main consumer unit (fuse box) to see if a circuit breaker has tripped
Your boiler has become too hot and has automatically shut down for safety purposes.
Why it happens: This fault occurs when the water inside your boiler reaches an unsafe temperature, triggering a safety switch to cut the power. It is often caused by a failing pump that can no longer move heat away from the boiler quickly enough or a buildup of limescale and sludge that restricts water flow. In some cases, the safety sensor itself may have developed a fault and is wrongly reporting that the unit is overheating.
Ensure all radiator valves are fully open to allow water flowLocate the reset button or switch on the boiler control panelPress the reset button once; if the light returns immediately, do not attempt further resets
Your boiler is failing to light the gas flame or cannot detect that the flame has started, so it has shut down for safety.
Why it happens: This fault occurs when the boiler tries to start but fails to either generate a spark or open the gas flow to create a flame. The most common reasons are a worn-out ignition electrode that can no longer create a spark or a faulty gas valve that isn't letting fuel into the burner.
Check if other gas appliances, like a cooker hob, are working to ensure gas is reaching the property.Verify that your gas pre-payment meter (if applicable) has credit.Turn the boiler selector switch to 'Reset' for 5 seconds, then back to the heater/hot water setting.
Your boiler has likely experienced an internal electrical fault or a component failure that has caused a safety fuse on the main control board to blow.
Why it happens: This fault occurs when an electrical surge or a component failure causes a safety fuse on the main control board to blow, cutting power to prevent further damage. The most common reason is a seizing water pump that is drawing too much current or a short-circuit within the boiler's internal wiring. As a result, the boiler shuts down completely to protect its sensitive electronic parts.
Full guide for F2on the Glow-worm Ultimate3 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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
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