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Vaillant Boiler F.70 Error Code
Invalid device code after a repair on Vaillant boilers.
VaillantAll Vaillant boiler codes
The boiler doesn't recognize what model it is. You'd normally only see this after an engineer has replaced the PCB and the display together, and the device number hasn't been entered again.
Compatible models
The installation manuals for the ecoTEC plus VU GB 656/4-5 A and the VU 126 to 356/6-5 OVZ boilers list it.
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.
How to fix Vaillant F.70
Call back whoever did the repair
If an engineer recently swapped the main board or display, let them know. Entering the device code is part of finishing that repair.
When to call a technician
Only an engineer can set the product code in the installer menu. It isn't something to try yourself.
Parts linked to F.70
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.70 code?
The installation manuals for the ecoTEC plus VU GB 656/4-5 A and the VU 126 to 356/6-5 OVZ boilers list it.
Can I fix Vaillant F.70 myself?
Only the outside checks. The steps above are the ones Vaillant's user instructions allow; if they don't clear F.70, 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.10Temperature sensor short circuit
- 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.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.