First let me come right out and say that I am a software guy and this seems like a hardware problem, so I already feel out of my league. That said, here's the deal:
Background: I have two-zone "hot air" heating in my home driven by air handlers in my garage which generate heat from propane stored in an underground tank near my driveway. There are two thermostats, both of the new touch-screen type. (I'm pretty sure the thermostats are installed correctly. One was installed professionally, and both respond properly to the fan controls.)
The Problem: Sometimes, like about 40% to 50% of the time, the temperature in one or both of the zones drops way below the target temperature. This is worse overnight, since I'm not awake to notice it and make a temporary fix. The temporary fix? Simply switching the thermostat off and then on again. When I do that I can hear a "click" and soon after that warm air is blowing from my floor and wall vents.
I guess there is an intermittent failure to communicate between my thermostats and the air handlers. What I don't understand is why, when the temperature is below the target temperature, the thermostats don't resend the "call for heat" signal. The thermostat clearly knows the ambient temperature, as it displays it. Why does it take a "reboot" to resend the signal? And the larger question, of course: how do I fix it?