BoilerFaultCodesTechnical description
Control box or the heat control module (HCM) is defective – HCM or control box connections need to be checked
What causes this fault?
This fault occurs when the boiler's internal computer chips lose the ability to speak to each other, often due to a hardware failure on the circuit board or a loose internal wiring connection. The most common reason is that the Heat Control Module, a small plug-in component that stores the boiler's identity, has worn out or become corrupted over time.
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.
Find a Gas Safe engineer
Search the official register →