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Vaillant Boiler F.10 Error Code
Temperature sensor short circuit on Vaillant boilers.
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A temperature sensor is reading as shorted. F.10 is the flow NTC thermistor and F.11 the return one; the cause is a failed sensor or a short in its cable.
Compatible models
From the fault table in the ecoTEC plus VU 126 to 356/6-5 OVZ manual. Vaillant doesn't say which other ranges use it.
Also shown as
F.11 covers the return sensor. F.00 and F.01 are the open-circuit versions of the same sensors.
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.
How to fix Vaillant F.10
Power it off and on
Turn the boiler off for a minute and back on. A code that returns straight away won't fix itself.
When to call a technician
Replacing a sensor or tracing a damaged cable means opening the boiler, which is for a Gas Safe engineer.
Parts linked to F.10
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.10 code?
From the fault table in the ecoTEC plus VU 126 to 356/6-5 OVZ manual. Vaillant doesn't say which other ranges use it.
Can I fix Vaillant F.10 myself?
Only the outside checks. The steps above are the ones Vaillant's user instructions allow; if they don't clear F.10, the fix is inside the boiler and needs a Gas Safe registered engineer (RGII in Ireland).
Other Vaillant boiler codes
- F.22Water pressure in the heating system is too low
- F.28Boiler failed to light
- F.29Flame went out and the boiler couldn't relight
- F.20Overheat safety cut-out has tripped
- F.23Too big a gap between flow and return temperature
- F.24Temperature rising too fast
- F.25Flue gas temperature too high
- F.27Flame detected with the burner off
- F.75No pressure rise when the pump starts
- F.00Flow or return temperature sensor not reading
- F.13Hot water cylinder sensor short circuit
- F.32Fan speed out of range
- F.61Gas valve control fault
- F.62Flame took too long to go out
- F.68Unstable flame
- F.70Invalid device code after a repair
- F.83Dry fire: no temperature change when the burner lit
Last reviewed 2026-10-21. Codes and steps can vary by model; check your owner's manual.