Medium Warning
D.28 on Vaillant ecoTEC plus Regular

Your boiler has detected a communication problem or a wiring fault with an external control accessory, such as an additional pump or zone valve.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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 control board loses communication with a specific internal relay that manages external components like your central heating pump. It is usually caused by a loose connection in the wiring harness or a component on the circuit board that has failed over time. In some cases, an electrical surge or moisture ingress may have damaged the sensitive electronic links between these parts.

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.27View →

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