Its not been working for a long time.
I am using a one wire temperature sensor for soil and everything else (soil related) records correctly, except for $avtempnovnowsoil, which then corrupts the monthly mean figures.
This was a reply you sent to another post back in February 2016
“you cant view a .inf data file, its a binary file
it looks like with the new version of WD (post build 81) I lost the source code for saving this soil temperature data
I will have to add that back in
(hence why its reading 0)”
I have tested here (I have a soil temperature with my davis station) and the custom tag
%avtempnovnowsoil%
works correctly (via the data file monthextrav2p112017.inf)