BoilerFaultCodes D.28 Medium Warning
Your boiler is having trouble communicating with an external control or smart home accessory, which might prevent your heating or hot water from turning on correctly.
Book a service
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: Switching accessory relay 2
What causes this fault?
This fault occurs when the boiler's main internal computer loses communication with an external control box or smart home wiring module. The most common reason is a loose connection in the wiring or a technical failure within the accessory module itself that tells the boiler when to turn on and off.
Typical repair cost £120-250 (including labour)
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like D.28 — no call-out fees, no surprises.
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