F.75 High

Vaillant F.75 Fault Code

Also written as F75 — same fault.

The Vaillant F.75 fault code means: your boiler is unable to detect a change in water pressure when the pump starts up, preventing it from firing up for heating or hot water.. It appears on 42 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: No pressure rise was detected on turning on the pump | Water pressure sensor or/and pump defective, Air in the heating system, quick bleeder defective, Too little water in appliance; check adjustable by-pass; connect external expension vessel to return

What causes the Vaillant F.75 fault?

This fault occurs when the boiler's internal computer fails to see a small 'jump' in water pressure that should happen every time the pump starts spinning. The most common reasons are a pressure sensor blocked with sludge or a pump that has seized up after a period of inactivity, meaning the system can't verify that water is circulating safely. In some cases, it can also be caused by the system pressure simply being too low for the sensor to register any movement.

This issue is frequently seen at the start of autumn when homeowners turn their heating back on for the first time, as the pump can seize up after sitting idle all summer.

Typical repair cost £180-450 (including labour)

DIY fix possible

Check the boiler pressure gauge and top it up to 1.5 bar if it is too lowEnsure all radiator valves and isolation valves under the boiler are fully openReset the boiler to see if the pump restarts

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Vaillant models that show the F.75 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant F.75 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026