F.75
Pressure change too low when pump starts
The boiler does not detect the expected pressure response when the pump starts.
What this code means
The boiler does not detect the expected pressure response when the pump starts.
Possible causes
- System pressure too low
- Air in boiler or heating system
- Water pressure sensor fault
- Pump or circulation problem
- Valve or blockage problem
Common symptoms
- F.75 displayed
- Boiler may lock out
- Heating or hot water may fail
Checks to make
- Check system pressure on the user display
- Follow the user manual for safe repressurisation if appropriate
- Arrange professional diagnosis if pressure is normal or the code returns
Safety
- Do not remove the boiler casing. Internal pump, pressure-sensor and gas-appliance work requires competent qualified personnel.
Model notes
Vaillant associates this with pressure response, circulation, pump and sensing faults.