BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off for safety because it has reached an excessively high temperature, likely due to a circulation problem.
Why it happens: This fault occurs when the water inside the boiler gets too hot, causing a safety sensor 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 blockage within the pipework that restricts flow. In some cases, the sensor itself may have developed a fault and is incorrectly reporting a high temperature.
Check that your radiator valves are fully open and not turned down.Ensure there is enough water pressure in the system by checking the gauge.Try resetting the boiler by pressing the reset button to see if it clears the lockout.
Your boiler has failed to ignite and has shut itself down for safety, meaning you will not have any heating or hot water until it is reset or repaired.
Why it happens: This fault occurs when the boiler's control system attempts to light the burner but fails to detect a flame after several attempts. The most common reasons include a lack of gas reaching the unit, a worn-out component failing to create a spark, or a sensor that can no longer confirm the flame is safely lit.
Check if your gas meter has credit and other gas appliances like the hob are workingPress the Reset button (indicated by a flame with a cross through it) for five secondsEnsure the boiler pressure gauge is between 1.0 and 1.5 barIf it is freezing outside, check that your white plastic condensate pipe hasn't frozen
Your boiler has detected that the water pressure is too low to operate safely and has shut down to prevent damage.
Why it happens: This fault occurs when the system lacks enough water pressure to circulate heat safely, causing the boiler to shut down to protect the heat exchanger. The most common reason is a slow leak somewhere in your radiators or pipework, or simply that the system needs to be topped up after air was bled from the radiators.
Locate the filling loop (usually a silver flexible hose) underneath the boiler.Open the one or two small valves on the hose until you hear water flowing.Watch the pressure gauge and close the valves when the needle reaches 1.5 bar.
Your boiler has switched itself off because the internal exhaust gases have reached a temperature that is too high, often caused by a circulation problem or a lack of water.
Why it happens: This fault occurs when the sensors detect that the exhaust gases leaving the boiler are getting much hotter than they should be, triggering an automatic safety shutdown. The most common reason is that heat isn't being moved away from the burner quickly enough, usually due to a lack of water pressure, a failing pump, or a blockage in the main heat exchanger.
Check the boiler pressure gauge and top it up to 1.5 bar if it is too lowEnsure all radiator valves are fully open to allow water to flowTry resetting the boiler once the system has cooled down
Your boiler has detected a problem with the sensor that measures the temperature of the water leaving the unit, causing it to shut down as a safety precaution.
Why it happens: This fault occurs when the boiler's internal computer loses communication with the sensor that monitors the temperature of the water being sent to your radiators. The most common reason is that the sensor has electronically failed or the internal wiring connecting it to the control board has become loose or damaged. Because the boiler no longer knows how hot the water is, it shuts down to prevent the system from overheating.
Full guide for F10Your boiler has lost its memory of whether it is a 24kW or 30kW model, meaning it cannot operate safely until its settings are re-programmed.
Why it happens: This fault occurs when the boiler's main control board loses the specific software settings that tell it which model it is currently operating. This is usually caused by a sudden electrical surge or a technical malfunction within the Printed Circuit Board's memory chip. Without this identity information, the boiler shuts down as a safety precaution because it doesn't know how much gas to burn.
Full guide for F43on the Glow-worm Ultracom 35 Store
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