Medium
D.28 on Vaillant Combi Compact 242EB

Your boiler's internal control board is having trouble communicating with an optional plugin component, usually related to external heating controls.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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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

DIY fix possible

Turn off the power to the boiler at the fused spur switchWait for 30 secondsTurn the power back on and check if the code clearsEnsure your external thermostat or programmer is powered and has fresh batteries

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Related fault codes

D.27View →F.27View →F.62View →

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