High
F.75 on Vaillant ecoFIT Pure 435

Your boiler has detected that the water pressure isn't rising correctly when the internal pump starts up, which usually points to low system pressure, trapped air, or a faulty sensor.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

Fault: No pressure change detection when starting pump — Water pressure sensor and/or pump defective, air in the heating installation, insufficient water in the product; check adjustable bypass, connect external expansion vessel to the return

From this model's manual
Verified against the Vaillant/Vaillant Ecofit Pure 412 435 Open Vent 0020230535 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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Related fault codes

F.22View →F.73View →F.74View →

All 71 fault codes on the ecoFIT Pure 435

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

conF.00F.01F.10F.11F.13F.22F.23F.24F.25F.27F.28F.29F.32F.49F.61F.62F.63F.64F.65F.67F.68F.70F.71F.72F.73F.74F.76F.77F.83F.84F.85F.87F.88F.89F.97S.0S.01S.02S.03S.04S.05S.06S.07S.08S.20S.21S.22S.23S.24S.25S.26S.27S.28S.30S.31S.32S.34S.39S.42S.46S.53S.54S.88S.91S.96S.98S.99S.108S.109

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