Is my thermostat incompatible?

expert EXPERT April 26, 2007

The story is complicated and we can't answer it completely without more facts. We do not know the model number of your set back thermostat, nor do we know how the controls on your heating system are wired. Because you have 3 zone valves, your system could be wired in a number of ways. For example, many systems with 3 zone valves, have three thermostats -- one for each zone. Some configurations measure outdoor air temperature while others maintain a specific water temperature within the system, relying on the zone valves to send the hot water to the zones where it is required. Thermostats also work at a specific voltage (typically 24 volts) and a certain current which is usually a fraction of an amp. Zone valves draw more current when they are opening and closing, and consequently this current may not be compatible with the current requirements of the thermostat. To further complicate things, your 3 zone valves may be wired in parallel or in series. Conventional thermostats also contain an anticipator. It sees that your house is heating up, realizes that your house will continue to heat after the boiler is shut off (because of all of the latent heat stored in the water and the radiators), and shuts off your boiler earlier, in anticipation of your home reaching its desired temperature. Some set back thermostats do not have a conventional anticipator and therefore may not be compatible with a zone valve that was built with an anticipator in mind. If you go to the web site of the zone valve manufacturer, you will find specifications for your specific zone valve as well as a list of recommended, compatible thermostats. We think that this is your best bet.