BoilerFaultCodesTechnical description
Control box is defective – HCM needs checking as it might not be inserted properly or need replacing
What causes this fault?
This fault occurs when the boiler's main control board loses communication with a specific chip called the Heat Code Module, which contains the boiler's 'identity' and safety settings. The most common reason is that this module has vibrated loose or has suffered an electrical failure, meaning the boiler can no longer verify which model it is and shuts down for safety.
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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