BoilerFaultCodesFerroli F34 Fault Code
The Ferroli F34 fault code means: your boiler is not receiving enough electricity from the mains supply to operate its electronic components safely.. It appears on 14 Ferroli models in our database.
Technical description: Supply voltage under 170v – electric supply error
What causes the Ferroli F34 fault?
This fault occurs when the electrical current entering your boiler drops to an unsafely low level, preventing the internal computer from functioning. The most common reason is a wider problem with the local power grid or a fault in your home's electrical wiring, though a failing internal circuit board can sometimes misread a healthy supply.
This fault can occasionally occur during extreme winter peaks when the national grid experiences exceptionally high demand, leading to temporary 'brownouts' or voltage drops.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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A cover plan would handle faults like F34: no call-out fees, no surprise bills.
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Ferroli models that show the F34 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atlas D Repair: £120-250
- Bluehelix HiTech RRT Repair: £100-350
- Bluehelix Pro RRT Repair: £120-250
- Bluehelix Tech RRT Repair: £100-£350
- Bluehelix Tech RRT 34C Repair: £120-250
- Energy Top B Repair: £120-250
- Extrema C Repair: £120-250
- Force W Repair: £100-250
- i25 Repair: £100-250
- i29 Repair: £120-250
- Maxima 35 S Repair: £120-250
- Modena HE Repair: £100-350
- Optimax HE 31 C Repair: £120-250
- Optimax HE Plus Repair: £120-250
Source
Ferroli F34 fault code information on this page is sourced and cross-checked against the official Ferroli service / installation manuals for each affected model.
- Ferroli Atlas D manual (PDF)
- Ferroli Bluehelix HiTech RRT manual →
- Ferroli Bluehelix Tech RRT manual →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026