BoilerFaultCodesVaillant F.68 Fault Code
Also written as F68 — same fault.
The Vaillant F.68 fault code means: your boiler is struggling to keep its flame steady, which is preventing it from staying on and heating your home.. It appears on 27 Vaillant models in our database.
Technical description: Fault: Flame signal unstable - Flame monitor reports an unstable flame signal
What causes the Vaillant F.68 fault?
This fault occurs when the boiler's control system cannot detect a consistent, healthy flame after the burner has ignited. The most common reasons are a worn-out sensing probe that can no longer 'see' the flame, or a gas valve that isn't delivering a steady flow of fuel to keep the burner lit.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
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A cover plan would handle faults like F.68: no call-out fees, no surprise bills.
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Vaillant models that show the F.68 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 412 Repair: £150-300
- ecoFIT Pure 418 Repair: £150-350
- ecoFIT Pure 425 Repair: £150-350
- ecoFIT Pure 435 Repair: £100-250
- ecoFIT pure 612 Repair: £150-300
- ecoFIT pure 615 Repair: £150-300
- ecoFIT pure 618 Repair: £150-300
- ecoFIT pure 630 Repair: £150-300
- ecoFIT Pure 825 Repair: £180-350
- ecoFIT Pure 830 Repair: £150-300
- ecoFIT Pure 835 Repair: £150-350
- ecoFIT sustain 415 Repair: £120-£250
- ecoFIT sustain 418 Repair: £120-£250
- ecoFIT sustain 430 Repair: £120-£250
- ecoFIT sustain 615 Repair: £150-300
- ecoFIT sustain 618 Repair: £150-300
- ecoFIT sustain 630 Repair: £150-300
- ecoFIT sustain 825 Repair: £150-300
- ecoFIT sustain 830 Repair: £150-300
- ecoFIT sustain 835 Repair: £150-300
- ecoTEC plus Repair: £100-£250
- ecoTEC pro Repair: £100-250
- ecoTEC sustain Repair: £120-£350
- Home Combi 25 Repair: £150-300
- Home Combi 30 Repair: £150-300
- Home Combi 35 Repair: £150-300
- Home Regular 12
Source
Vaillant F.68 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 435 manual (PDF)
- Vaillant ecoFIT pure 630 manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026