BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because it cannot detect a flame, meaning it has safely shut down to prevent gas from flowing without being burned.
Why it happens: This fault occurs when the boiler's control system fails to confirm that a flame has been successfully lit after a sequence of attempts. The most common reasons include a lack of gas reaching the burner, worn-out sparking electrodes that fail to ignite the fuel, or a dirty sensor that can no longer 'see' the flame even if it is actually present.
Check that your gas emergency control valve (usually by the meter) is in the 'on' positionCheck if other gas appliances in your home, such as a hob, are working correctlyPress the reset button on the front control panel to see if the boiler restarts
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature limit, triggering a safety sensor to cut the power. The most common reasons are a failed pump that isn't moving water away fast enough or a blockage in the heat exchanger that traps heat. Sometimes, it can also be caused by a build-up of air or sludge in the system restricting flow.
Check that your radiator valves are open to allow water to flowEnsure the system pressure is within the normal range (usually 1 to 1.5 bar)Locate the manual reset button on the control box and press it firmly
Your boiler has become too hot and has automatically shut down to prevent damage to the internal components.
Why it happens: This fault occurs when the water temperature inside the boiler exceeds a safe limit, causing the safety sensors to shut the unit down to prevent damage. The most common reasons include a failing system pump that isn't moving water away from the heat exchanger fast enough or a buildup of sludge and debris that has restricted the flow of water.
Locate the overheat reset button under the control box flapPress the button firmly to reset the safety thermostatCheck that all radiator valves are open and the system pressure is correct
Your boiler has tried to start up several times but cannot establish a stable flame to begin heating.
Why it happens: This fault occurs when the boiler's control system cannot confirm that a flame has successfully ignited after five attempts. It is usually caused by a worn-out ignition component that fails to create a spark or a faulty sensor that cannot detect the heat of the fire, leading the boiler to shut down for safety. In some cases, it may also indicate that gas is not reaching the burner at the correct pressure.
Full guide for Detection FaultYour boiler has encountered an internal timing error or electrical communication fault because it didn't enter the correct setup mode when its gas control valves were being linked.
Why it happens: This fault is physically caused by an electrical communication error between the boiler's control board and the gas valves during a startup or reset sequence. It typically happens when the system fails to synchronise its safety checks, often due to a loose connection or a failing wiring harness that prevents the components from 'handshaking' correctly. In many cases, this indicates that the internal electronics can no longer reliably control the flow of gas, leading the boiler to shut down for safety.
Full guide for fault conditionYour boiler's temperature sensor has stopped working correctly, meaning the system can no longer tell how hot the water is and has shut down as a precaution.
Why it happens: This fault occurs when the internal sensor responsible for monitoring water temperature becomes damaged or loses its ability to send an accurate electrical signal. The most common reasons are electrical failure within the thermistor itself or corrosion on the wiring connections caused by years of heat cycling.
Full guide for C/H Sensor Faulton the Ideal Concord CXC 48 116
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