High
D.75 on Vaillant Atmomax

Your boiler is taking too long to heat up your hot water cylinder, which usually means there is a problem with the sensor or the water flow between the boiler and the tank.

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

Maximum charging time for a storage without own controller

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.20View →F.22View →F.24View →

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