Vaillant F.22 and F.75 fault codes — low pressure or pump sensor fault
⚠️ This needs a qualified professional
This fault involves gas or mains electrical work. Don't attempt a DIY repair — UK law requires gas work to be carried out by a Gas Safe registered engineer. Below is what to check and describe to them, not step-by-step repair instructions.
F.22 and F.75 are related but distinct Vaillant fault codes, both tied to the boiler’s water pressure system rather than gas or ignition.
F.22 — low system pressure
Check the pressure gauge — if it’s below roughly 1 bar, this is very likely your cause. Repressurise via the filling loop following your manual’s exact steps, to around 1-1.5 bar when cold. If you’re topping up regularly (weekly or more often), there’s a leak somewhere in the system that repressurising alone won’t fix — see our separate guide on boilers losing pressure repeatedly.
F.75 — pump pressure sensor fault
This means the boiler’s sensor didn’t detect an expected pressure change when the pump started. If your pressure gauge reads normally (1-1.5 bar) but F.75 persists, this points more towards a failing pump or pressure sensor, or trapped air in the system, rather than simply needing repressurising.
⚠️ This needs a Gas Safe engineer
Repressurising via the filling loop (following your manual) is the one safe DIY step for F.22. Beyond that — and for F.75 specifically, which usually points to a component fault rather than pressure alone — don’t attempt further diagnosis or open the boiler casing. Both faults need a qualified heating engineer, and Vaillant recommends an annual service specifically because sludge and limescale build-up makes both codes more likely as a system ages.