Technical description
MAINS ON
What causes this fault?
This is not actually a fault, but a status indicator showing that your boiler has a healthy electrical supply. It means the appliance is sitting in standby mode and is simply waiting for a signal from your thermostat or programmer to start heating your home. If your heating isn't coming on while this light is showing, the issue is likely with your external controls rather than the boiler itself.
DIY fix possible
Check that your external room thermostat or programmer is turned up and calling for heatEnsure the boiler control knob is not set to the 'Off' positionWait a few minutes to see if the boiler begins its ignition sequence automatically