High
D.26 on Vaillant Atmomax

Your boiler's electronic control board is having trouble communicating with an internal switch that manages external components like a pump or valve.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Additional relay control ecoTec

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.27View →F.61View →F.62View →

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