Emergency
F04 on Ferroli Optimax HE 31 C

Your boiler has detected that hot combustion gases are not venting away correctly and has safely shut down to prevent the risk of carbon monoxide poisoning.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

What the manual says

Manufacturer manual

Fume thermostat or generic safety activation

From this model's manual
Verified against the Ferroli/Ferroli Optimax He 31 C 4726742 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a emergency 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

F05View →F37View →

All 32 fault codes on the Optimax HE 31 C

Seeing a different code? Every code this model can display, in one place.

A01A02A03A04A05A06A41F05F07F10F11F12F13F14F15F20F21F24F34F35F37F39F40F41F42F43F47F50F51Low system pressureNo burner ignition

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