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 28 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.
- Atmomax Repair: £90-180
- ecoFIT Pure 412 Repair: £150-300
- ecoFIT Pure 418 Repair: £150-300
- ecoFIT Pure 425 Repair: £150-300
- ecoFIT Pure 435 Repair: £150-300
- ecoFIT Pure 825 Repair: £120-250
- ecoFIT Pure 830 Repair: £120-250
- ecoFIT Pure 835 Repair: £150-300
- ecoTEC Repair: £90-250
- ecoTEC 65kW Repair: £120-250
- ecoTEC exclusive Repair: £90-180
- ecoTEC Plus 610 Repair: £120-250
- ecoTEC Plus 615 Repair: £100-250
- ecoTEC Plus 620 Repair: £100-250
- ecoTEC Plus 625 Repair: £100-250
- ecoTEC Plus 630 Repair: £100-250
- ecoTEC Plus 635 Repair: £100-250
- ecoTEC Plus 826 Repair: £120-250
- ecoTEC Plus 840 Repair: £100-250
- ecoTEC Plus 938 Repair: £100-250
- ecoTEC Pro Repair: £120-£450
- ecoTEC Pro / ecoTEC Plus Repair: £100-£250
- ecoTEC Pro 24 Repair: £120-£450
- ecoTEC Pro 28 Repair: £120-£450
- ecoTEC Pro 30 Repair: £150-300
- ecoTEC sustain Repair: £100-250
- Home Combi Repair: £120-250
- Home System Repair: £120-450
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 412 manual (PDF)
- Vaillant ecoFIT Pure 835 manual (PDF)
- Vaillant ecoTEC manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026