David, pop the front off your thermostat, there should be a small fuse. Pull the fuse and leave it out for a minute or so and then replace. Sometimes this will reset your thermostat.
Also, are you aware of DOAI (Discovery Owners Association)? DOAI forum is second to none. great group of very knowledgeable Discovery owners. Here is a link to DOAI site.
https://www.discoveryowners.com/
Jim Pinkerton
2018 Discovery 40D