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 (usually a flexible silver hose) underneath or near the boiler.Slowly open the valve or valves on the loop until you hear water entering the system.Watch the pressure gauge and close the valves tightly once the needle reaches between 1.0 and 1.2 bar.
Your boiler has detected that there is too much water pressure in the system, which has caused it to shut down for safety.
Locate a radiator bleed valve and use a radiator key to carefully release water into a container.Monitor the boiler pressure gauge until it drops down to approximately 1.2 bar.Tighten the bleed valve and reset the boiler to clear the fault code.
Your boiler is failing to light the flame properly, meaning it cannot heat your home or water.
Check that your gas emergency control valve and meter are turned onCheck if other gas appliances in your home, like a hob, are working correctlyPress and hold the 'R' reset button for 2-3 seconds to restart the ignition sequence
Your boiler has likely overheated, causing a safety sensor to shut it down to prevent damage.
Check that all radiator valves are open and not blockedBleed all radiators to remove trapped air from the systemTurn the boiler off and back on to attempt a reset once it has cooled down
Your boiler has stopped working because the waste water pipe is backed up or blocked, preventing the unit from draining safely.
Check the plastic pipe leading from the boiler to the outside for signs of freezing or ice blockages.If frozen, pour warm (not boiling) water over the external pipe to melt the ice.Ensure the internal drainage trap (siphon) isn't visibly clogged with debris if accessible.
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 untouched for at least one full hour.Once the hour has passed, the 'AL 28' code should disappear automatically.Attempt one final reset; if the original fault returns, do not try to reset it again and call a gas safe engineer.
on the Sime Murelle EV 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