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Vaillant Boiler F.24 Error Code

Temperature rising too fast on Vaillant boilers.

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F.24
May need a pro

Heat is building up in the boiler quicker than it should, a sign that water isn't moving through it properly. The manual blames a blocked or weak pump, air in the boiler, low system pressure or a non-return valve that's stuck or fitted the wrong way.

Compatible models

Found in the fault table of the ecoTEC plus VU 126 to 356/6-5 OVZ installation manual. Vaillant doesn't publish a wider list, so check the manual for your boiler.

Also shown as

No other codes are listed for this fault.

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.24

  1. Look at the gauge

    If pressure is low, top it up to about 1.5 bar following your operating manual.

  2. Reset after a short wait

    Give the boiler a few minutes to settle, then hold reset for more than 3 seconds.

When to call a technician

Pressure fine and F.24 keeps showing: a Gas Safe engineer should check the pump and purge air from inside the boiler.

Parts linked to F.24

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.24 code?

Found in the fault table of the ecoTEC plus VU 126 to 356/6-5 OVZ installation manual. Vaillant doesn't publish a wider list, so check the manual for your boiler.

Can I fix Vaillant F.24 myself?

Only the outside checks. The steps above are the ones Vaillant's user instructions allow; if they don't clear F.24, 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