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 has become too hot and has automatically shut down to prevent damage or safety issues.
Why it happens: This fault occurs when the water inside the heat exchanger reaches a temperature that is dangerously high, triggering a safety switch to cut off the gas. The most common reasons are a pump failure preventing water from moving through the system or a blockage caused by a build-up of sludge and debris. It can also be caused by a faulty sensor that is incorrectly reporting the temperature to the control board.
Wait for the boiler to cool down completely (at least 30 minutes).Check that all radiator valves are open and not blocked.Press the overheat reset button located on the controls behind the front panel.Check if the pump is running or if there is a system blockage if it trips again.
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 tried to fire up five times without success and has shut itself down for safety.
Why it happens: This fault occurs when the boiler cannot detect a flame after several attempts to start. The issue is typically caused by a lack of gas reaching the burner, a faulty ignition system failing to create a spark, or a dirty sensor that cannot confirm the fire is actually lit.
Check if other gas appliances (like a hob) are working to confirm gas supplyEnsure your gas meter has credit if you use a prepay meterPress the 'Reset' button on the control panel to try and clear the lockout
Your boiler has switched itself off because it became too hot, acting as a safety precaution to prevent damage.
Why it happens: This fault occurs when the internal water temperature exceeds a safe limit, causing the boiler to shut down to prevent internal melting or component failure. The most common reasons are a lack of water flow caused by a failing pump or an airlock, though it can also be triggered if the sensors themselves become faulty.
Check that your radiator valves are open and not blockedEnsure there is enough water pressure in the system (if applicable)Locate the overheat reset button under the control panel cover and press it firmly
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 Faulton 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