Vaillant eco plus 531 boiler?

F.70 is shown because the boiler doesn't know what it is.
Press + and i together to show d.0, press minus(-) to get to d.97,
press i and display will show 0, press + until boiler shows 17,
long press i until 17 stops flashing and display returns to d.97,
now press minus to get to d.93 and press i, there will be a number displayed.
The number displayed tells you boiler what it is (model etc).
You need to look at the data badge underneath the boiler, look for (vcw-286 r-3/3), that is just an example, but your boiler will look similar to the number format I have listed.
Look in the literature that comes with the pcb and look for your country symbol (GB IT FR etc depending where you are).
Now look for the corresponding number that matches your boiler (vcw xxxx),
to the right there will be a number from 1-9 (by memory),
this number must be entered when reaching d.93 (earlier), then press i until number entered stops flashing, press reset and boiler will reboot an fixed.
Simple innit!

Carefree
November 2022