BoilerFaultCodesThe 6 most common faults
Your boiler has shut itself down as a safety precaution because the water inside has become far too hot.
Why it happens: This fault occurs when the internal temperature of the boiler exceeds safe limits, triggering a safety switch to prevent damage. It is usually caused by a failure to move hot water away from the heat exchanger, often due to a seized pump, a blockage in the pipework, or a faulty sensor misreading the temperature.
Wait at least 15 to 30 minutes for the boiler to cool down completely.Ensure all radiator valves are fully open and there is no air trapped in the system.Locate the manual reset button on the control panel, press it firmly, and see if the boiler restarts.
Your boiler is failing to start because it cannot successfully ignite the gas after several attempts.
Why it happens: This fault occurs when the boiler tries to light the gas but cannot detect a stable flame, causing the system to shut down for safety. The most common reasons are that the spark isn't strong enough to ignite the fuel, the sensors are too dirty to 'see' the flame, or the gas valve isn't opening correctly to let fuel into the burner.
Check that your gas emergency control valve is turned onIf you have a prepayment meter, check that you have sufficient creditCheck that other gas appliances in your home, such as a hob, are working correctlyPress the reset button on the control panel to try once more
Your boiler has lost its ability to accurately measure the temperature of the water being heated for your radiators, causing it to stop running as a safety precaution.
Why it happens: This fault occurs when the internal sensor responsible for monitoring your central heating temperature fails to send a reliable signal to the main control board. The most common reason is that the sensor's internal electrical resistance has drifted out of range or the component has suffered a complete electrical failure due to age. In some cases, loose or damaged wiring between the sensor and the controller can also trigger this shutdown.
Full guide for C/H Sensor FaultYour boiler has detected that water is failing to circulate correctly through the system, which will prevent it from heating your home or providing hot water.
Why it happens: This fault occurs when the boiler's internal sensors detect that water is not moving through the heat exchanger at the required rate, often due to a mechanical failure or a blockage. The most common reason is a seized or worn-out circulation pump, though it can also be caused by air trapped in the system or a build-up of sludge obstructing the flow. Without this movement, the boiler must shut down to prevent the unit from overheating and causing internal damage.
Full guide for PumpYour boiler has detected an issue with its internal sensors and has stopped running to prevent any damage or incorrect temperature readings.
Why it happens: This fault occurs when the boiler's internal sensors stop communicating correctly with the main control board. It is usually caused by an electrical failure within the sensor itself or a loose connection in the wiring that prevents the boiler from safely monitoring water temperature. Because the boiler cannot tell how hot the water is getting, it shuts down as a safety precaution.
Full guide for Boiler sensorYour boiler is unable to safely control the flow of gas needed to stay lit, so it has shut down to avoid a potential hazard.
Why it happens: This fault occurs when the boiler's internal computer detects that the gas valve is failing to open or close correctly during the ignition process. The most common reasons are a mechanical failure within the valve assembly, a burnt-out electrical coil, or a loose connection in the wiring harness that prevents the valve from receiving power.
Full guide for Gas valve(s)on the Ideal Concord CXA 40-120
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 Ideal 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