BoilerFaultCodesVaillant F.88 Fault Code
Also written as F88 — same fault.
The Vaillant F.88 fault code means: your boiler has detected an electrical connection issue with the gas valve, meaning it cannot safely ignite to provide heating or hot water.. It appears on 33 Vaillant models in our database.
Technical description: Fault: Gas valve assembly. Gas valve assembly not connected or it is connected incorrectly, short circuit in the cable harness
What causes the Vaillant F.88 fault?
This fault occurs when the boiler's internal computer loses electrical communication with the gas valve, which is the component responsible for releasing fuel into the burner. The most common reason is a loose or damaged wiring connection between these parts, though it can also be caused by a complete electronic failure within the gas valve itself.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like F.88: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Vaillant models that show the F.88 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 412 Repair: £200-350
- ecoFIT Pure 418 Repair: £200-350
- ecoFIT Pure 425 Repair: £200-350
- ecoFIT Pure 435 Repair: £200-350
- ecoFIT pure 612
- ecoFIT pure 615
- ecoFIT pure 618
- ecoFIT pure 630
- ecoFIT Pure 825 Repair: £200-350
- ecoFIT Pure 830 Repair: £180-300
- ecoFIT Pure 835 Repair: £200-350
- ecoFIT sustain 415
- ecoFIT sustain 418
- ecoFIT sustain 430
- ecoFIT sustain 615
- ecoFIT sustain 618
- ecoFIT sustain 630
- ecoFIT sustain 825
- ecoFIT sustain 830
- ecoFIT sustain 835
- ecoTEC plus 412 Repair: £180-350
- ecoTEC plus 415 Repair: £180-350
- ecoTEC plus 418 Repair: £180-350
- ecoTEC plus 424 Repair: £180-350
- ecoTEC plus 430 Repair: £180-350
- ecoTEC Plus 610 Repair: £180-350
- ecoTEC Plus 620 Repair: £180-350
- ecoTEC Plus 625 Repair: £180-350
- ecoTEC Plus 635 Repair: £180-350
- ecoTEC Plus 840 Repair: £180-350
- ecoTEC sustain Repair: £180-350
- Home Combi Repair: £200-350
- Home System Repair: £250-£450
Source
Vaillant F.88 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
- Vaillant ecoFIT Pure 425 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoFIT pure 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026