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Vaillant Boiler F.75 Error Code

No pressure rise when the pump starts on Vaillant boilers.

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F.75
May need a pro

Each time the pump starts, the boiler expects to see the pressure jump a little. It didn't. Low water, air in the system, a flat or faulty expansion vessel, a failed pressure sensor or pump, or a broken sensor cable can all cause it.

Compatible models

Vaillant's UK fault code page lists F.75 without naming models. Check your ecoTEC manual to confirm it applies to yours.

Also shown as

Vaillant's UK fault page calls it a heat pump start in one place and the heating pump in another; the causes it lists are the boiler's own pump and pressure sensor.

Difficulty

Try the basic checks, but the usual fix is a technician's job.

Not sure you are reading the code right? See how to read Vaillant boiler codes.

Safety first: never take the casing off a gas boiler. If you smell gas, open windows, don't use light switches, turn the gas off at the meter if you can and call your gas emergency number from outside. A carbon monoxide alarm going off means the same: switch the boiler off, get fresh air and call.

How to fix Vaillant F.75

  1. Check and top up the pressure

    If the reading is below 0.8 bar, refill to around 1.5 bar using the filling loop the way the operating manual explains.

  2. Bleed the radiators

    Air makes this code more likely. Bleed each radiator, nearest the boiler first, then look at the gauge again and top up if it has dropped.

  3. Reset

    Press and hold reset for longer than 3 seconds, then give the pump a few minutes to run.

When to call a technician

Pressure right, air out and F.75 still shows: the pump, pressure sensor or expansion vessel needs testing by a Gas Safe engineer.

Parts linked to F.75

These are the parts an engineer usually checks for this code. They sit inside the sealed casing, so leave them to a Gas Safe registered engineer.

Frequently asked questions

Which Vaillant models show the F.75 code?

Vaillant's UK fault code page lists F.75 without naming models. Check your ecoTEC manual to confirm it applies to yours.

Can I fix Vaillant F.75 myself?

Only the outside checks. The steps above are the ones Vaillant's user instructions allow; if they don't clear F.75, the fix is inside the boiler and needs a Gas Safe registered engineer (RGII in Ireland).

Other Vaillant boiler codes

Last reviewed 2026-10-21. Codes and steps can vary by model; check your owner's manual.

Sources we checked