BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system has dropped too low and needs to be topped up.
Locate the filling loop (the flexible silver hose usually found underneath the boiler).Open the one or two small valves on the loop slowly until you hear water flowing.Watch the pressure gauge and close the valves once the needle reaches between 1.0 and 1.2 bar.
Your boiler has shut down because it has detected it is getting too hot, which is usually caused by air trapped in the system or a circulation problem.
Check that your radiator valves are fully openGently bleed your radiators to remove any trapped airEnsure the system pressure is between 1.0 and 1.5 barAttempt to reset the boiler using the control knob
Your boiler is struggling to detect a flame, which prevents it from firing up to provide heating or hot water.
Check that your gas emergency control valve is in the 'on' positionCheck if other gas appliances in your home, like a hob, are working correctlyPress the reset button once to see if the boiler restarts
Your boiler has stopped working because water is backing up inside the system, likely due to a blocked or frozen external drainage pipe.
Check the white plastic pipe leading outside for any blockages or iceIf frozen, pour warm (not boiling) water over the external pipe to melt the iceEnsure the internal trap or siphon isn't visibly clogged with debrisPress the reset button to see if the error clears
Your boiler has been manually reset too many times in a short period and has temporarily locked itself for safety.
Leave the boiler powered on and wait for at least one hour without touching any buttons.Once the lockout period has passed, the error should clear or allow one further reset.If the boiler locks out again immediately, do not attempt further resets and call a Gas Safe engineer.
Your boiler is repeatedly failing to keep a flame lit, meaning it cannot provide heating or hot water for your home.
Check that your gas emergency control valve is in the 'on' positionIf you have a prepayment meter, check that you have sufficient creditTest another gas appliance, like a hob, to ensure gas is reaching your homeReset the boiler following the manufacturer instructions
on the Sime Murelle Pro HE MkII Combi
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 Sime 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.
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