Amazingly I had the same problem but would never have noticed the corrosion on those connectors (just one in my case) unless you had suggested this.
I now have perfect thermostat operation!
Thanks for your eagle eyes in spotting that and for posting!
Hi there,
Interested to see this discussion, I am having exactly the same problem...
My thermostat has been working perfectly since it was installed 5 years ago, a couple of months ago battery signal flashing so replaced those and worked well again now suddenly the last few days not doing...