99 High
Your boiler's main control panel has lost connection with the internal computer, meaning they can no longer talk to each other to operate the heating.
Technical description: Communication MMI -ESYS lost
Typical repair cost: £150-£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 99 — no call-out fees, no surprises.
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Parts commonly replaced
- MMI (User Interface) Board
- Main PCB
- Wiring Harness
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