Unknown
F.74 on Vaillant ecoFIT sustain 835

Vaillant ecoFIT sustain 835 fault code F.74

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

What the manual says

Manufacturer manual

Fault: Electrical problem in the water pressure sensor: Line to water pressure sensor has a short circuit to 5V/24V or internal fault in the water pressure sensor

From this model's manual
Verified against the Vaillant/Vaillant Vaillantpro Ecofit Sustain Combi Installation And Maintenance In 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like F.74: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

All 42 fault codes on the ecoFIT sustain 835

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

ConnectionF.00F.01F.10F.11F.12F.13F.20F.22F.23F.24F.25F.27F.28F.29F.32F.49F.61F.62F.63F.64F.65F.67F.68F.70F.71F.72F.73F.75F.76F.77F.78F.83F.84F.85F.86F.87F.88F.89F.91F.97

Related guides you might find useful

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

New boiler cost 2026

Realistic UK prices for a swap.

Read →