I have a chronotherm III

I have a chronotherm III unit with zoned heating. First floor and second floor have their own unit with on/off controls. Basement unit and sunroom unit are "slave units" tied to the first floor master unit. These units have their own temperature control settings but are dependent on first floor unit for on/off control.

Basement unit is set for heat at 62 but is heating up to as high as 78. Tried bypassing programming system (sleep, wake, leave, return) and setting it on "Hold" heat at 62. Doesn't help and what I found is that system automatically switches to a reading of "Hold-cool" and a setting of 65.

I have had 2 HVAC companies look at the system. One suggested the "Hold" solution. They checked the dampers and said the thermostat was working. They now want to use a camera to see if the problem is deeper than they can see with the eye.

By the way, the other "slave unit" in the sunroom (it's not sunny - I live in Pittsburgh!) also switches to Hold-cool after I set it to Hold heat. The temp in that room is also warmer than the setting.