High
F35 on Ferroli Optimax

Your boiler has detected an issue with the quality of your home's electrical supply, meaning the power entering the unit is inconsistent.

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

Irregular mains frequency

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

F34View →F37View →F40View →

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