BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure is too low and needs to be topped up.
Locate the filling loop, which is usually a flexible silver hose under the boiler.Slowly open the small valve (or valves) on the hose to let water into the system.Watch the pressure gauge and close the valves once the needle reaches between 1.0 and 1.2 bar.
Your boiler has tried to light but cannot detect a flame, which means it has locked itself out for safety.
Check that your gas emergency control valve is open and other gas appliances are working.If you have a pre-pay gas meter, check that you have sufficient credit.Press the reset button on the boiler control panel to see if the fault clears.
Your boiler has overheated, causing it to shut down automatically for safety.
Check that all radiator valves are open to ensure water can flow.Follow the boiler's manual to bleed any air out of your radiators.Wait for the boiler to cool down and try pressing the reset button.
Your boiler is struggling to detect a flame, which means it cannot stay lit to provide heating or hot water.
Check that your gas emergency control valve is in the 'on' positionVerify if other gas appliances in your home, such as a hob, are receiving gasPress and hold the reset button for a few seconds to see if the boiler restarts
Your boiler has detected a problem with the temperature sensor that monitors the water being sent to your radiators, which prevents the system from heating up safely.
Full guide for AL 05Your boiler has lost communication with the internal gas control system, meaning it cannot provide heating or hot water until the electrical connection is restored.
Full guide for AL 11on the Sime Ecomfort Plus HE EV 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