7 Day Programmable Hydronic Heating Thermostat, TH140-28-01-B

I've purchased three of these thermostats for our hydronic baseboard heating system to replace the original mercury thermostats. They work well, look good and appear to be very well made. Please note that these thermostats do not have a backlight. If you absolutely need a backlit display, look elsewhere. Since they are programmable, I've found the lack of backlighting to be only a minor annoyance. Also, there is no on/off switch, although they have a "vacation" button that effectively serves the same purpose by turning the temperature setting down. Although these are listed as Honeywell Home brand thermostats, the devices and packing all say Aube. Apparently Aube is owned by Honeywell. Also, although they're marketed for hydronic systems, they're actually general purpose thermostats that will work with pretty much any heating system that uses 24, 120 or 240 volt controls. They do have a couple of hydronic-specific options: There is a setting that will briefly activate the pump once a day in the summer to prevent it from seizing, and they also support an optional floor temperature sensor. The thermostats are configured with a number of DIP switches. These set the temperature display units (F or C), time format (12 or 24 hour) and other options. There are two modes of operation: proportional and conventional. In proportional mode, the thermostat learns the optimum length of time to operate, while in conventional mode it uses the traditional anticipation where the system is shut off before the set temperature is reached. With each mode, there are options to tune the thermostat for the specific type of heating system. Programming is fairly simple. Only two preset temperatures are supported, plus a third preset for vacation mode. Up to four time periods per day may be programmed. You can program all days of the week at once, or program individual days. The thermostats require two AA batteries for operation.

We have floor radiant heat but we use a wood stove a lot. I have replaced our simple old thermostats with a couple of these and they seemingly worked great. When I got around to changing the one in our master bedroom I noticed that it was clicking (turning on and off) very frequently. Checking it out I noticed that when it turned the heat on the displayed room temperature went up about half a degree per minute, even well before the the hot water was reaching the room. So then it would turn the heat off after only a couple minutes. I spent a lot of time trying to figure out if something about my wiring was causing the problem. Finally I just removed the thermostat from the wall (and base plate with the wiring). I set it on a dresser and it behaved the same way, rising temperature when it turned the heat on - even disconnected from the system wiring. It's like something inside the thermostat was generating heat. Testing several of these the same way I find they all act the same. Honeywell tech support could offer no ideas except that they are defective. But they come from several orders over several years. I can't help thinking this must be something solvable but I give up and I'm returning all of them (5) that can still be returned. I see another review talks about unpredictable on and off cycles - perhaps that was the same problem.