BoilerFaultCodesThe 6 most common faults
Your boiler has detected that the water pressure is too low, causing it to stop working for safety.
Locate the filling loop (the flexible silver hose usually found under the boiler).Slowly open the one or two small tap valves on the hose until you hear water flowing.Watch the pressure gauge and close the valves tightly once the needle reaches between 1.0 and 1.5 bar.
Your boiler has tried to start but could not detect a flame, likely because gas isn't reaching the burner or the ignition spark is failing.
Press and hold the 'R' or reset button to see if the error clears.Check that your gas meter is in credit and that other gas appliances like a hob are working.Verify that the gas isolation valve under the boiler is fully open.
Your boiler has shut down because it has detected it is getting too hot, often caused by a lack of water flow or trapped air.
Check that the boiler pressure is between 1.0 and 1.5 barEnsure all radiator valves and isolating valves are fully openGently bleed your radiators to release any trapped airPress the 'Reset' button on the control panel
Your boiler has failed to light the gas and has locked itself for safety, which means you currently have no heating or hot water.
Check that your gas meter is topped up with credit and the main gas lever is on.Ensure other gas appliances in your home, like a hob, are working correctly to confirm gas flow.Press and release the 'Reset' button to clear the red light and restart the ignition sequence.
Your boiler has detected that water is not circulating correctly or has become too hot, causing it to shut down for safety.
Check that all radiator valves are fully openEnsure the central heating system pressure is between 1.0 and 1.5 barPress the reset button to see if the fault clears
Your boiler has stopped working because the water pressure inside your heating system has dropped too low.
Locate the external filling loop, which is a silver braided hose connecting two pipes near your boiler.Open the valves at both ends of the hose to allow mains water into the system.Monitor the pressure gauge on the front of the boiler until the needle reaches between 1.0 and 1.5 bar, then securely close both valves.
on the Sime Murelle HE System
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