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 silver filling loop (braided hose) usually found underneath the boiler.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 failed to light the flame or cannot detect that the burner is on, meaning your heating and hot water will not work.
Check if your gas supply is active by testing other gas appliances like a hobCheck if your gas meter has credit (if using a pre-payment meter)Hold the 'R' or reset button for a few seconds to see if the boiler restarts
Your boiler has overheated, prompting a safety switch to shut the system down to prevent damage.
Check that all radiator valves are fully open to allow water flowCheck the system pressure gauge and top up to 1.5 bar if it is lowTurn the selector switch to the reset position for a few seconds and then back to 'ON'Bleed your radiators to remove any trapped air pockets
Your boiler has detected a fault with the temperature sensor that monitors the water leaving the unit, meaning it cannot safely regulate the heat and has stopped working.
Full guide for AL 05Your boiler is struggling to detect a flame, meaning it cannot stay on safely to provide heating and hot water.
Full guide for AL 08Your boiler has lost communication with the component that controls the gas flow, meaning it cannot safely ignite to provide heating or hot water.
Full guide for AL 11on the Sime Ecomfort System Plus HE EV
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