What does the Vaillant F.75 fault code mean?

Your boiler is locking out because it cannot detect the water pressure rising when the internal pump starts up.

How much does it cost to fix Vaillant error code F.75?

Typical repair cost for the Vaillant F.75 fault is £150-350 including labour.

Manufacturer manual

Fault, no pressure change detection when starting pump

From this model's manual

Verified against the Vaillant/Vaillant Ecotec Plus 937 07 2012 Isim installation & service manual.

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Boiler cover options

A cover plan would handle faults like F.75: no call-out fees, no surprise bills.

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Seeing a different code? Every code this model can display, in one place.

1 to 1.5 bar when cold on most UK boilers, from the manuals.

Quarter turn on the valve, wait for water, then check the boiler pressure.

On a combi it is usually the diverter valve. On a system boiler, the motorised valve.