BoilerFaultCodesThe 6 most common faults
01
Red LED on (solid) High DIY-safe
Your boiler has failed to light the gas and has locked itself out for safety.
What to try first
Check that your gas emergency control valve and meter are turned onIf you have a prepayment meter, ensure you have credit availablePress the reset button once to see if the boiler restarts
02
Red LED after flow switch High DIY-safe
Your boiler has stopped because its internal safety sensors have detected that water is either not moving through the system or is becoming too hot.
What to try first
Check that your system pressure is between 1 and 1.5 bar on the pressure gauge.Ensure all radiator valves and any isolation valves under the boiler are fully open.Try restarting the boiler by turning the selector switch to the 'reset' position for a few seconds.
03
Flashing orange LED High Engineer
Your boiler is struggling to move water through your heating system, which means it has stopped heating your home or water to prevent damage.
Full guide for Flashing orange LED04
Red LED on (after safety stat) High Engineer
Your boiler has switched itself off because it has detected that it is getting too hot or there is a problem with the flue gases.
Full guide for Red LED on (after safety stat)05
LED flashing after fan High Engineer
Your boiler has stopped working because the internal fan, which safely clears exhaust fumes, is not starting or running correctly.
Full guide for LED flashing after fan06
Orange LED flashing High Engineer
Your boiler has detected an issue with the sensor that monitors the temperature of the water circulating through your radiators.
Full guide for Orange LED flashingon the Sime Ecomfort System 25 HE
Ignition electrodeGas valveIgnition leadPrinted Circuit Board (PCB)Circulation 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