BoilerFaultCodesYour boiler is confused because it is trying to communicate with an external control box that isn't compatible with its current setup.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: wrong configuration with accessory | link box VR65 connected to combination boiler
What causes this fault?
This fault occurs when the boiler's main control board detects an external wiring box that was designed for older hot water systems but is not compatible with your specific boiler model. It essentially creates a digital 'clash' where the boiler receives signals it doesn't understand, leading it to shut down for safety. The most common reason is that an incorrect accessory was installed or the boiler's internal software has been configured for a system type that doesn't match the physical parts attached.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A boiler cover plan would cover faults like F.78 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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