Ferroli · Optimax 25 S

F35 boiler fault code

Optimax 25 S

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What F35 means

Irregular mains frequency.

Gas Safe engineer: The code remains or returns after the step above, or no home step applies; arrange diagnosis by a Gas Safe registered engineer.

A boiler fault code alone is not a gas or carbon-monoxide emergency. If you smell gas, a CO alarm sounds, or someone has possible carbon-monoxide symptoms, leave and call 0800 111 999 from outside.

Safe check

Note the code shown on the display. Do not open, adjust or repeatedly reset the boiler. Contact a Gas Safe registered engineer.

When to contact an engineer

The code remains or returns after the step above, or no home step applies; arrange diagnosis by a Gas Safe registered engineer.

Source and provenance