BoilerFaultCodesThe 6 most common faults
Your boiler has sensed that the temperature is rising too quickly or unevenly, which usually means water isn't flowing through the system as it should.
Why it happens: This fault occurs when the heat generated by the burner cannot be carried away from the heat exchanger quickly enough, leading to a rapid heat spike. The most common reason is a failed circulation pump or a blockage in the system, such as sludge or debris, which prevents the water from moving. It can also be caused by a faulty sensor giving an incorrect temperature reading to the boiler's computer.
Check that your radiator valves are openEnsure the boiler pressure is between 1 and 1.5 bar on the gaugeGently bleed your radiators to remove any trapped air
Your boiler has detected a problem with either its internal water pressure or its temperature safety sensors, which has caused the system to stop working.
Why it happens: This fault occurs when the boiler’s safety controls detect that either the internal water pressure has dropped too low or the exhaust gases have become too hot. It is often triggered by a leak in the system reducing pressure, or a build-up of debris causing the heat exchanger to overheat. In some cases, the sensors themselves may have physically failed or lost their connection to the main control board.
Check the pressure gauge on the front of the boilerIf the pressure is below 1.0 bar, use the filling loop to top it up to 1.5 barPress the reset button and wait for the boiler to restart
Your boiler has shut down because it has detected that the water inside is getting too hot, which is often caused by a blockage or a pump failure.
Why it happens: This fault occurs when the water leaving the boiler exceeds its safe temperature limit, causing the system to shut down to prevent damage. It is usually caused by a failure in the circulation pump or a physical blockage within the internal pipework that stops heat from moving away from the burner. In some cases, a faulty sensor may also be incorrectly reporting that the water is overheating.
Check that all radiator valves are fully openCheck that the boiler pressure is between 1.0 and 1.5 barReset the boiler by turning the mode dial to the 'RESET' position for two seconds
Your boiler has shut down because the water returning to the unit is too hot, typically meaning the heat isn't being distributed around your home properly.
Why it happens: This fault occurs when the water traveling back into the boiler is nearly as hot as the water leaving it, indicating that heat isn't being transferred to your radiators. The most common reasons are a failed pump that isn't circulating the water or a blockage in the system, such as a build-up of sludge or closed radiator valves.
Ensure all radiator valves (TRVs) are fully open to allow water to circulate.Check that your external heating pump is running if you have a separate system pump.Reset the boiler by following the instructions on the control panel.
Your boiler is overheating because the water inside is heating up too quickly, often caused by a lack of circulation or a blockage.
Why it happens: This fault occurs when the water inside the boiler heats up at an unsafe speed, causing the system to shut down to prevent damage. The most common reason is that the water isn't moving through the unit properly, often due to a pump failure, trapped air, or a buildup of sludge blocking the pipework.
Check that all radiator valves are fully openCheck that the boiler pressure is between 1.0 and 1.5 barRestart the boiler to see if the fault clears
Your boiler's internal computer has encountered a critical electronic error and can no longer control the heating or hot water safely.
Why it happens: This fault occurs when the boiler's main control board suffers a hardware failure and can no longer process signals or safety checks. It is often caused by electrical surges, moisture ingress from a small leak, or simple component wear and tear over time. Because the 'brain' of the boiler is damaged, it shuts down instantly to prevent unpredictable behavior.
Full guide for 400on the Ideal Response SE
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