BoilerFaultCodesVaillant F.73 Fault Code
Also written as F73 — same fault.
The Vaillant F.73 fault code means: your boiler has lost the ability to monitor its own water pressure due to a sensor or wiring fault, causing the system to shut down for safety.. It appears on 28 Vaillant models in our database.
Technical description: Water pressure sensor signal out of range (too low) | Cable to water pressure sensor is broken or has a short-circuit at 0 V or water pressure sensor defective
What causes the Vaillant F.73 fault?
This fault occurs when the boiler's internal computer loses communication with the component that measures water pressure. The most common reason is a failed digital sensor that has worn out internally or a break in the thin wires connecting that sensor to the main control board. Because the boiler can no longer verify if there is enough water to operate safely, it shuts down to prevent overheating.
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.73 fault code
Click a model for the full fault code list and model-specific repair notes.
- ecoFIT Pure 412 Repair: £150-250
- ecoFIT Pure 418 Repair: £150-250
- ecoFIT Pure 425 Repair: £150-250
- ecoFIT Pure 435 Repair: £90-180
- ecoFIT pure 612 Repair: £150-250
- ecoFIT pure 615 Repair: £150-250
- ecoFIT pure 618 Repair: £150-250
- ecoFIT pure 630 Repair: £150-250
- ecoFIT Pure 825 Repair: £150-250
- ecoFIT Pure 830 Repair: £150-250
- ecoFIT Pure 835 Repair: £150-250
- ecoFIT sustain 415 Repair: £150-250
- ecoFIT sustain 418 Repair: £150-250
- ecoFIT sustain 430 Repair: £150-250
- ecoFIT sustain 615 Repair: £150-250
- ecoFIT sustain 618 Repair: £150-250
- ecoFIT sustain 630 Repair: £150-250
- ecoFIT sustain 825 Repair: £120-220
- ecoFIT sustain 830 Repair: £120-220
- ecoFIT sustain 835 Repair: £120-220
- ecoTEC exclusive Repair: £140-£250
- ecoTEC plus Repair: £140-£220
- ecoTEC plus VU GB 656/4-5 A Repair: £150-250
- ecoTEC pro Repair: £140-£220
- ecoTEC sustain Repair: £130-220
- Home Combi 25 Repair: £150-250
- Home Combi 30 Repair: £150-250
- Home Combi 35 Repair: £150-250
Source
Vaillant F.73 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