BoilerFaultCodesTechnical description
Failure in the electrical supply to the boiler; check fuses and 230V mains input.
What causes this fault?
This fault occurs when the boiler is receiving main power but isn't getting the specific 230V command to actually start heating. The most common reason is a failure in an external component like a broken room thermostat, a blown fuse in the wiring center, or a motorized valve that is stuck and failing to trigger the microswitch. Essentially, the boiler is 'waiting' for a signal that never arrives because of a break in the electrical chain outside the unit itself.
This issue is frequently seen during the first cold snap of autumn when heating systems are turned on for the first time after being idle all summer, often revealing a seized zone valve or a thermostat with dead batteries.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.