Vaillant F75 Fault Code: Causes, Fixes & Reset Guide
If your Vaillant boiler is displaying the F75 fault code, it means the safety cut-out has triggered because the pump feedback does not match the pressure sensor feedback. In plain English, your boiler has detected a problem with the water pressure or the pump — and it has shut itself down for safety.
What the F75 fault code means
The F75 code is Vaillant's way of telling you that the boiler's safety system has detected a mismatch between what the pump is doing and what the water pressure sensor is reading. This is a safety mechanism designed to prevent the boiler from running dry or damaging itself.
Possible causes of the F75 fault
- Pump defective — The pump may have failed or be running too slowly to circulate water properly.
- Water shortage in the system — Your system pressure may have dropped too low.
- Air in the heating installation — Trapped air can cause the pump to run dry and the pressure sensor to give false readings.
- Water pressure sensor defective — The sensor itself may be faulty and giving incorrect readings.
Can you fix it yourself?
There are a few things you can check before calling an engineer:
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Check your system water pressure — Look at the pressure gauge on the front of your boiler. If the needle is below 1.0 bar, the system needs repressurising. Use the filling loop to slowly bring the pressure up to between 1.0 and 1.5 bar.
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Bleed your radiators — Trapped air is one of the most common causes of the F75 fault. Use a radiator key to bleed each radiator, starting from the one furthest from the boiler and working your way back.
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Reset the boiler — After repressurising and bleeding, try resetting the boiler. If the fault clears and stays away, you've likely fixed the issue.
If the pressure keeps dropping after topping up, or the F75 code returns after resetting, the pump or water pressure sensor is likely defective and you'll need a Gas Safe registered engineer.
When to call a professional
Do not keep resetting the boiler if the F75 fault recurs — this is a safety device and repeatedly resetting it could cause further damage. If you've repressurised the system, bled the radiators, and the fault persists, it's time to call in a professional.
A Gas Safe registered engineer will be able to test the pump, check the water pressure sensor, and diagnose whether the issue is with the pump itself, the sensor, or the PCB.
Need help with your Vaillant boiler?
Sanju's Heating covers Newbury, Basingstoke and Reading. We're Gas Safe registered and can diagnose and repair Vaillant F75 faults quickly with transparent pricing.
Call us on 01635 74 50 40 or book online at sanjusheating.co.uk/book
You can also check our full Vaillant fault code guide for help with other Vaillant error codes.
