BoilerFaultCodesYour boiler's internal communication system has detected an issue or a duplicate identity on its data network, which can sometimes happen after a power cut or part change.
This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.
Technical description: LON user number
What causes this fault?
This fault occurs when the boiler's internal communication network becomes confused by seeing multiple components with the same identification number or when a signal is blocked. The most common reason is an electronic glitch following a power surge, or a conflict that arises after a technician has replaced a control board without reconfiguring its digital address.
DIY fix possible
Locate the 'Reset' button or menu option on the control panel.Perform a full system reset as per the user manual.Turn the power off at the fused spur switch for 30 seconds, then turn it back on.
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A boiler cover plan would cover faults like 77:1 — no call-out fees, no surprises.
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