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 flexible filling loop (braided hose) underneath or near the boiler.Slowly open the small handles on the valves 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 is failing to light properly because it cannot detect a flame, which means you have no heating or hot water.
Check that your gas emergency control valve is in the 'on' positionVerify if other gas appliances in your home, like a hob, are working correctlyAttempt to reset the boiler by turning the selector switch to the 'R' position for a few seconds
Your boiler has switched itself off because it has detected that it is getting too hot, likely due to a blockage, trapped air, or a faulty safety sensor.
Check that your radiator valves are open and not turned off.Bleed your radiators to remove any trapped air from the system.Check the boiler pressure gauge and top it up to 1.5 bar if it is low.Reset the boiler using the control knob.
Your boiler is struggling to detect a flame, which means it cannot stay lit to provide heating or hot water.
Check if other gas appliances, like a cooker, are working to ensure gas is reaching the propertyCheck that your gas meter has credit if you use a prepay systemReset the boiler by turning the selector switch to the reset position for a few seconds
Your boiler has stopped working because water is not moving around the system properly, which is preventing it from heating up safely.
Check that your system pressure is between 1 and 1.5 bar on the pressure gauge.Ensure all radiator valves and isolation valves under the boiler are fully open.Try bleeding your radiators to remove any trapped air that might be blocking flow.
Your boiler has stopped working because the waste water pipe is backed up or frozen, preventing the system from draining safely.
Check the white plastic pipe exiting the house for signs of ice or blockageThaw a frozen pipe by pouring warm (not boiling) water over it or using a heat packEnsure the internal drainage trap is clear and the pipe is not kinkedReset the boiler once the blockage is removed
on the Sime Halstead Trio
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