BoilerFaultCodesThe 5 most common faults
01
Red LED on (solid) High DIY-safe
Your boiler has failed to light the gas and has locked itself for safety, which is why it is currently not providing heating or hot water.
What to try first
Check that your gas meter is turned on and you have credit if using a pre-payment meterCheck if other gas appliances in your home, like a hob, are working correctlyHold the reset button for a few seconds to see if the boiler restartsIf the boiler is in a cold location, check that the white plastic condensate pipe outside isn't frozen
02
Red LED after flow switch High DIY-safe
Your boiler has stopped working because water is not moving through the system correctly, causing it to shut down to prevent overheating.
What to try first
Check that your boiler pressure is between 1.0 and 1.5 barEnsure all radiator valves and isolation valves are fully openTry resetting the boiler using the selector dial
03
Red LED on (after safety stat) High Engineer
Your boiler has shut down because it has detected an unsafe build-up of heat or a blockage in the flue system.
Full guide for Red LED on (after safety stat)04
LED flashing after fan High Engineer
Your boiler has identified a problem with the fan that clears exhaust gases, preventing the system from starting up for safety reasons.
Full guide for LED flashing after fan05
Orange LED flashing High Engineer
Your boiler has detected a problem with the temperature sensor that manages your central heating, meaning it cannot accurately measure how hot the water is.
Full guide for Orange LED flashingon the Sime Planet Super 4 WM
Ignition ElectrodeGas ValveFlame Sensing ProbePCBCirculation 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