F.75
Vaillant
No Pressure Rise Detected When Pump Starts
F.75 displayed at startup, boiler does not fire, pump may run briefly
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Air in system or pump, Seized or blocked pump, Faulty water pressure sensor, Very low system pressure
How to Fix / Troubleshooting
Safety: Allow the system to cool before bleeding or topping up.
Steps:
- Check system pressure and top up via the filling loop to the recommended level.
- Bleed radiators and the boiler's automatic air vent to remove trapped air.
- With power off, remove the pump vent plug (if fitted) and manually rotate the pump shaft to free it.
- Restore power and reset the boiler; listen for the pump starting.
- If F.75 persists, the pressure sensor may not be detecting the pressure change; consider replacing the water pressure sensor.
If the pump is not running or is noisy, it may need replacement by a heating engineer.
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Repair Difficulty
Medium
3/5
Required Part
Circulation Pump
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