BoilerFaultCodesVaillant F.74 Fault Code
Also written as F74 — same fault.
The Vaillant F.74 fault code means: your boiler has detected a problem with the sensor that monitors water pressure, meaning it cannot accurately tell if there is enough water in the system to run safely.. It appears on 21 Vaillant models in our database.
Technical description: Water pressure sensor signal outside correct range, the sensor signal is too high
What causes the Vaillant F.74 fault?
This fault occurs when the boiler's internal computer receives an electrical signal from the water pressure sensor that is completely outside of its expected range. The most common reason is that the sensor itself has developed an internal electrical short or has become blocked with system debris, causing it to send a false high-voltage reading. In some cases, a damaged or damp wiring harness can also interfere with the signal being sent to the main control board.
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.74 fault code
Click a model for the full fault code list and model-specific repair notes.
- Atmomax Repair: £130-210
- ecoFIT Pure 412 Repair: £150-250
- ecoFIT Pure 418 Repair: £150-250
- ecoFIT Pure 425 Repair: £150-250
- ecoFIT Pure 435 Repair: £150-250
- ecoFIT Pure 825 Repair: £150-250
- ecoFIT Pure 830 Repair: £180-350
- ecoFIT Pure 835 Repair: £150-250
- ecoTEC Repair: £140-£220
- ecoTEC 65kW Repair: £150-300
- ecoTEC exclusive Repair: £140-£260
- ecoTEC Plus 826 Repair: £180-350
- ecoTEC Plus 938 Repair: £120-200
- ecoTEC Pro Repair: £100-220
- ecoTEC Pro / ecoTEC Plus Repair: £140-£220
- ecoTEC Pro 24 Repair: £100-220
- ecoTEC Pro 28 Repair: £100-220
- ecoTEC Pro 30 Repair: £150-250
- ecoTEC sustain Repair: £120-200
- Home Combi Repair: £150-250
- Home System Repair: £140-£220
Source
Vaillant F.74 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