BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system has dropped too low and needs topping up.
Locate the filling loop (a flexible silver hose with small lever valves) underneath or near the boiler.Slowly open the valves until you hear water entering the system.Watch the pressure gauge and close the valves once the needle reaches between 1.0 and 1.2 bar.
Your boiler is failing to light properly, which means it cannot heat your water or radiators until the gas ignition issue is resolved.
Check that your gas meter is topped up and the emergency control valve is in the 'on' positionTest other gas appliances, such as a hob, to ensure gas is reaching your homePress the 'Reset' button on the boiler control panel to attempt a restart
Your boiler has overheated because the internal temperature has become too high, causing it to shut down for safety.
Check all radiator valves are open to ensure water can circulate.Try to bleed your radiators to remove trapped air from the system.Restart the boiler using the reset button once it has cooled down.
Your boiler has stopped working because waste water is backing up inside its drainage pipe, often due to a simple blockage or freezing.
Locate the plastic pipe exiting the boiler and leading outside.Check for any visible blockages or debris at the end of the pipe.If it is freezing cold, gently pour warm (not boiling) water over the external pipe to melt any ice.Clean the internal condensate siphon if you are comfortable removing the plastic trap.
Your boiler has failed to keep its flame lit several times in a row and has locked itself out for safety.
Check that your gas emergency control valve is in the open positionCheck if other gas appliances, like a cooker, are working to confirm gas supplyReset the boiler by turning the selector switch to the 'R' position for a few seconds
Your boiler has lost its connection to the external heating controls, meaning it cannot receive instructions on when to turn the heating on.
Check batteries in your wall-mounted thermostat or remote controlEnsure the thermostat is within range of the boiler and has not been movedReset the boiler by turning the selector switch to 'OFF/RESET' for 5 seconds and then back to 'ON'
on the Sime Dewy 30/130 HE FS
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