Agree on the MicroAir but that assumes there is actually something wrong with your tstat. There are a couple of other possibilities, but I would lean toward the tstat having an issue in this case because Zone 3 has a roof AC component in addition to an Aquahot component and you seem to have lost access to both. Turn off the salesman switch by the entry door and leave it off for 5 minutes, turn it back on and see if the problem persists. If so, it would be worth trying the MicroAir, it's plug and play and much more functional than the Airxcel unit. Your current model is probably an Airxcel 9330-333
Other possibilities are the AC controller (in the AC roof unit) or a wiring issue. The tstat communicates with the AC roof units via a two wire proprietary network. Here is some info on the tstat:
https://drive.google.com/file/d/11pB...w?usp=drivesdk
Note the Entegra's have a special Airxcel version not used by most other brands.
Here's is a blog post about my upgrade to the EasyTouch:
https://myquantumdiscovery.com/micro...llation-review