BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system is too low.
Locate the filling loop (usually a silver flexible hose) underneath the boiler.Slowly open the valve or valves on the filling loop to allow water into the system.Monitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the valves tightly.
Your boiler has detected that there is too much water pressure in the system, which can cause the safety valves to trigger or the unit to stop working.
Locate a radiator bleed valve and use a radiator key to release water into a container until the pressure gauge on the boiler drops to 1.2 bar.Check that the filling loop valves (the silver braided hose beneath the boiler) are fully tightened and not accidentally left open.Restart the boiler to see if the error code clears.
Your boiler is failing to light or stay lit because it cannot detect a flame, which has caused the system to shut down for safety.
Check if your gas supply is active by testing another gas appliance like a hobEnsure your gas meter has credit if you use a prepay or 'top-up' meterTry resetting the boiler by turning the selector knob to 'R' for a few seconds
Your boiler has overheated, causing it to shut down automatically to protect the internal components.
Check that all radiator valves are fully openCheck the boiler pressure is between 1 and 1.5 barBleed any air from your radiatorsPress the 'Reset' button on the control panel
Your boiler has detected that the water drain for condensation is backed up, meaning waste water cannot leave the system.
Check the plastic pipe leading from the boiler to the outside drain for signs of freezing or blockages.If the external pipe is frozen, gently pour warm (not boiling) water over it to melt the ice.Ensure the internal siphon/trap is clear of debris if it is easily accessible and removable.Reset the boiler once the blockage has been cleared.
Your boiler has been reset too many times in a short period and has temporarily locked itself for safety.
Wait for 60 minutes without touching any buttons to allow the lockout timer to expire.Ensure your gas supply is turned on and you have credit on your meter.Attempt one single reset once the hour has passed; if it fails again, call a gas safe engineer.
on the Sime Murelle Pro HE 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