Problem with Wirsbo thermostats

Jascott

I just purchased a condo with radiant floor heating. There are 6 circuits, each controlled by Two-wire Wirsbo heat only thermostats. When I moved in two weeks ago, one of the thermostats was "frozen" showing a temp of 72, a solid horizontal line under the temp and a heat icon under the line. Pushing either button alone or simultaneously did nothing. My only recourse was to pull one of the wires to reset it, after which everything was fine after I reconnected it. Two weeks later, I was showing my daughter how to operate the system, and found that 3 of the 6 thermostats were "frozen" and required the same fix. Any ideas?

4Johnpipe

You may have a bad transformer. There also were a defective batch of Uponor zone control boards about 2-3 years ago. The serial or batch number began with AA then some numbers all AA boards are defective.

hot_rod

what are the thermostats connected to? A relay box?

Jascott

I am on the road, but will be back early November and will check your suggestions and report back. Thanks for the help!