High
F15 on Saunier Duval Isofast

Your boiler is having trouble moving an internal valve that controls how hot water is sent to your taps or radiators, meaning it cannot properly switch between heating your home and your hot water supply.

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

Stepper motor fault

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

F14View →F16View →

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