F.75
Vaillant
No Pressure Change Detected on Pump Start (where fitted)
F.75 pump/flow detection fault; appliance does not start heating cycle
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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
Defective pump, Blocked or stuck pressure sensor, Air in system, Blocked primary circuit, Faulty pressure sensor wiring
How to Fix / Troubleshooting
Safety: Isolate power and gas. Allow the unit to cool.
- Bleed system: Bleed air from the pump and high points to ensure water is present.
- Check pump operation: Briefly power the unit and listen/feel for pump running. If silent or very noisy, the pump may be seized or worn and should be replaced.
- Inspect pressure sensor: Locate the water pressure sensor and check for blockage at the connection point. Clean or replace the sensor if clogged or faulty.
- Check wiring: Ensure the pressure sensor harness is intact and firmly connected.
- Reset and test: After repairs, reset the appliance and confirm that F.75 no longer appears when a cycle starts.
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Repair Difficulty
Hard
4/5
Required Part
Water Pressure Sensor
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