BoilerFaultCodesThe 6 most common faults
01
Red LED on (solid) High DIY-safe
Your boiler has failed to light the gas to create heat and has safely shut itself down to prevent a problem.
What to try first
Check that your gas emergency control valve (usually by the meter) is in the 'on' positionCheck if other gas appliances in your home, like a hob, are working correctlyPress and hold the reset button for a few seconds to see if the boiler restarts
02
Red LED after flow switch High DIY-safe
Your boiler has detected that water is not circulating correctly through the system, which has likely caused it to shut down to prevent overheating.
What to try first
Check that your boiler 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 resetting the boiler by turning the selector switch to the 'Reset' position.
03
Flashing orange LED High Engineer
Your boiler is struggling to move water through its system, which means it has safely shut itself down to prevent overheating.
Full guide for Flashing orange LED04
Red LED on (after safety stat) High Engineer
Your boiler has shut down because it or the flue has become too hot, and it has locked out for safety reasons.
Full guide for Red LED on (after safety stat)05
LED flashing after fan High Engineer
Your boiler is unable to start up safely because the internal fan, which clears waste gases, is not spinning correctly or communicating with the control board.
Full guide for LED flashing after fan06
Orange LED flashing Medium Engineer
Your boiler has detected a problem with the temperature sensor that controls your central heating, meaning it may not be able to warm your radiators correctly.
Full guide for Orange LED flashingon the Sime Ecomfort HE Combi
Ignition ElectrodeFlame Sensing ProbeGas ValvePCBCirculating PumpWater Flow Switch
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