Medium
D.27 on Vaillant Combi Compact 242EB

Your boiler's internal control system is struggling to communicate with an external accessory or control relay, which may affect how your heating or hot water turns on.

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 1

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

D.28View →F.27View →S.27View →

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