F.75
Vaillant
Pump / Pressure Sensor Interaction Fault
Boiler displays F.75, no pressure rise detected when pump starts
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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
Airlocked or failed pump, Blocked or faulty pressure sensor, System air or low water content, Blocked or frozen condensate affecting start-up
How to Fix / Troubleshooting
Safety: Isolate power before bleeding the pump. Water may be hot.
- Check system pressure: Ensure pressure is 1.0–1.5 bar. Top up if needed.
- Bleed pump: Remove the pump bleed screw carefully and allow air to escape until water flows. Refit screw.
- Listen for pump: On start-up, confirm the pump runs. If silent or just humming, it may be seized and require replacement.
- Check condensate pipe: In freezing weather, ensure the external condensate pipe is not frozen. Thaw gently with warm (not boiling) water and lag the pipe.
- Engineer tasks: If F.75 persists, the pressure sensor may be blocked or faulty and should be cleaned or replaced by a technician.
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Repair Difficulty
Medium
3/5
Required Part
Circulation Pump
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