BoilerFaultCodesVaillant F.49 Fault Code
Also written as F49 — same fault.
The Vaillant F.49 fault code means: your boiler has lost communication with its external controls, such as your thermostat, often due to an electrical wiring error or interference.. It appears on 29 Vaillant models in our database.
Technical description: eBUS undervoltage | Short circuit on eBUS, overload on eBUS or two power sources on eBUS with different polarity
What causes the Vaillant F.49 fault?
This fault occurs when there is an electrical conflict or a lack of power on the digital communication line that connects your boiler to your thermostat. It is usually caused by wires being accidentally crossed during installation, a physical short circuit in the cabling, or an internal electronic failure in the control module. Effectively, the boiler can no longer 'hear' what the thermostat is telling it to do, so it shuts down for safety.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the F.49 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: £150-300
- ecoFIT Pure 425 Repair: £150-300
- ecoFIT Pure 435 Repair: £100-£250
- ecoFIT pure 612 Repair: £120-250
- ecoFIT pure 615 Repair: £120-250
- ecoFIT pure 618 Repair: £120-250
- ecoFIT pure 630 Repair: £120-250
- ecoFIT Pure 825 Repair: £120-250
- ecoFIT Pure 830 Repair: £120-250
- ecoFIT Pure 835 Repair: £150-300
- ecoFIT sustain 415 Repair: £120-250
- ecoFIT sustain 418 Repair: £120-250
- ecoFIT sustain 430 Repair: £120-250
- ecoFIT sustain 615 Repair: £120-250
- ecoFIT sustain 618 Repair: £120-250
- ecoFIT sustain 630 Repair: £120-250
- ecoFIT sustain 825 Repair: £120-250
- ecoFIT sustain 830 Repair: £120-250
- ecoFIT sustain 835 Repair: £120-250
- ecoTEC exclusive Repair: £90-180
- ecoTEC plus Repair: £90-250
- ecoTEC plus VU GB 656/4-5 A Repair: £120-250
- ecoTEC pro Repair: £120-£450
- ecoTEC sustain Repair: £100-250
- Home Combi 25 Repair: £120-250
- Home Combi 30 Repair: £120-250
- Home Combi 35 Repair: £120-250
- Home Regular 12
Source
Vaillant F.49 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