BoilerFaultCodesThe 6 most common faults
Your boiler has likely detected that it is getting too hot and has paused operation as a safety precaution.
Check that your external pump is running and hasn't seized.Ensure all radiator valves are fully open to allow water to circulate.Check that the system pressure is between 1 and 1.5 bar.Reset the boiler by turning the selector switch to 'R' for five seconds.
Your boiler has paused because a safety switch or an external control has told it to stop running temporarily.
Check if your thermostat or programmer is set to 'ON' and calling for heat.Ensure any external bypass valves or safety switches haven't been accidentally tripped.Try resetting the boiler by turning the selector switch to 'R' for five seconds and then back to 'On'.
Your boiler is struggling to keep its flame lit, which is causing it to stop providing heating and hot water as a safety precaution.
Check if other gas appliances, like a hob, are working to ensure gas is reaching the propertyIf it is freezing outside, check that the white plastic condensate pipe leading outdoors hasn't frozenReset the boiler by turning the selector knob to the 'R' position for five seconds
Your boiler has switched itself off because it has become too hot internally, likely due to a circulation problem.
Ensure all radiator valves are fully open to allow water to flow.Check that your system pressure is between 1 and 1.5 bar on the gauge.Press the reset button or turn the selector switch to 'R' for 5 seconds.
Your boiler has failed to light after several attempts and has locked itself for safety.
Check that your credit or prepaid gas meter has sufficient funds.Ensure other gas appliances, such as a hob, are receiving gas.Turn the selector switch to the reset position for five seconds, then turn it back to your desired setting.
Your boiler has encountered an internal error and has locked itself out for safety, meaning it will not provide any heating or hot water until reset.
Turn the selector switch to the 'R' (Reset) position and hold it for at least five seconds.Release the switch and wait for the boiler to attempt to restart.Check that your gas pre-payment meter (if applicable) has credit and that the main gas lever is open.
on the Baxi 400 Heat
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 Baxi 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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
Affiliate links. We may earn a commission at no extra cost to you.