BoilerFaultCodesThe 6 most common faults
Your boiler has failed to ignite or lost its flame and has shut down as a safety precaution.
Why it happens: This fault occurs when the boiler tries to light but fails to detect a stable flame after several attempts. The most common reasons are a lack of gas supply to the appliance, a worn-out ignition spark, or a faulty sensor that cannot 'see' the flame even if it has lit.
Check that your gas pre-payment meter (if applicable) has credit.Ensure the gas isolation valve under the boiler is in the 'on' position.Press the 'Reset' button on the front of the boiler display for 2 seconds.
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 internal water temperature reaches an unsafe level, causing the boiler to shut down to protect its internal components. The most common reasons are a failed pump that isn't circulating the water, a blockage in the system, or a buildup of air that prevents heat from being carried away from the heat exchanger.
Check that your radiator valves are open and not turned to zero.Ensure there is enough water pressure in the system by checking the external filling loop gauge.Wait for the boiler to cool down and press the 'Reset' button on the front panel.
Your boiler has stopped working because the waste water pipe is likely blocked or frozen, causing water to back up into the unit.
Why it happens: This fault occurs when the liquid waste produced during the heating process cannot drain away from the boiler. The most common reason is a blockage in the drainage pipe or the internal trap, which causes water to back up into the heat exchanger and trigger a safety shutdown. Often, this happens because debris has built up over time or the pipe has become restricted.
Locate the plastic pipe leading from your boiler to the outside of your property.Check if the end of the pipe is blocked by debris or frozen ice.If frozen, pour warm (not boiling) water over the external pipe until the ice melt clears the blockage.Restart the boiler by pressing the reset button.
Your boiler has detected an internal error or has become too hot and has safely shut itself down as a precaution.
Why it happens: This fault occurs when the boiler's internal safety sensors detect that the water temperature has exceeded safe limits or if a component has failed. The most common reasons include a blockage in the system, a pump failure that prevents water from moving, or a build-up of limescale within the heat exchanger. Because the unit cannot safely cool itself down, it shuts off to prevent damage to the internal parts.
Locate the reset knob on the front control panel.Turn the knob to the 'RESET' position and hold it for 2 seconds.Return the knob to its original setting and wait for the boiler to restart.
Your boiler has detected an issue with the air pressure or water flow sensors, preventing it from firing up for safety.
Why it happens: This fault occurs when the boiler's internal sensors detect that either the water pressure is too low or the fan isn't moving air through the system correctly. For safety reasons, the boiler will refuse to ignite if it cannot confirm that water is flowing and harmful exhaust gases are being safely vented away. The most common reasons are a leak in the central heating system causing a drop in pressure, or a physical blockage in the air tubes or flue.
Full guide for ERROR CODE 3Your boiler is having trouble venting exhaust gases safely, which prevents it from firing up to provide heating or hot water.
Why it happens: This fault occurs when the boiler's internal safety sensors detect that the fan isn't moving enough air to safely clear exhaust gases from the system. It is usually caused by a failing fan motor, a blockage in the air pressure tubes, or debris caught in the flue that prevents a steady flow of air. Without this confirmed airflow, the boiler won't ignite to ensure carbon monoxide doesn't build up inside the unit.
Full guide for ERROR CODE 4on the Ideal Icos HE
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