Vaillant · Current Vaillant F-code boilers
F.75Pressure change too low when pump starts
This code applies to ecoTEC plus, ecoTEC plus remastered, ecoTEC pro, ecoTEC exclusive, ecoFIT pure. Fault codes narrow down the likely problem, but they do not replace a model-specific diagnosis.
What you can safely check
- Check the pressure gauge with the system cold.
- If it is below the range stated in the boiler manual, repressurise only by following that model's user instructions.
- Stop and book an engineer if pressure drops again, rises excessively, or there is a visible leak.
How an engineer may fix it
Check for leaks, trapped air, the pressure sensor, pump and expansion vessel; repair the underlying fault before recommissioning.
Vaillant states that meanings can vary by appliance. Confirm the exact model manual before acting.
Manufacturer source: Vaillant UK — Boiler fault codes list. Checked 15 August 2026. The appliance manual and an engineer’s on-site diagnosis take precedence. Never remove the boiler case yourself.