9U 233 High
Your boiler's main internal computer or memory chip has developed a communication fault or has failed, meaning the unit cannot safely control the heating process.
Technical description: Control box or heat control module (HCM) is defective or loose, the HCM needs to be checked
Typical repair cost: £250-£450 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Protect yourself from future repair bills
A boiler cover plan would cover faults like 9U 233 — no call-out fees, no surprises.
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Parts commonly replaced
- Heat Control Module (HCM)
- Printed Circuit Board (PCB)
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