BoilerFaultCodesTechnical description
Heat Control Module (HCM) error – problem with code plug
What causes this fault?
This fault occurs when the boiler's main control board loses its connection to the code plug, which acts like a memory chip containing the unit's specific settings. The most common reason is a physical failure of the chip itself or a loose connection on the circuit board caused by years of vibration and thermal expansion. Because the boiler no longer knows its own safety parameters, it shuts down immediately to prevent damage.
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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