Milivolt Systems w/ Modern Thermostats
Jesse Grandbois is one of the techs who reads the tech tips wrote a few tips that he wanted to share on some gas furnace control basics. This tip is about how to use a fancy digital stat on a millivolt system
For those of you who don’t know, a millivolt system uses a thermocouple / thermopile with a standing (constant) pilot flame to generate a tiny “millivolt” signal that is used to control the furnace rather than the 24v signal modern thermostats use.
On a call for heat the relay coil will be powered closing the SPST relay powering the millivolt system (NO terminals) for heat.