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 central brain and its memory chip stop talking to each other, often due to an electrical failure or a loose internal connection. The most common reason is that the Heat Control Module—a small plug-in component that stores the boiler's specific settings—has failed or become corrupted. When this link is broken, the boiler shuts down immediately as a safety precaution because it no longer knows how to operate the burner correctly.
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.
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