New thermostat

mm121244

Just purchased a new honeywell ct87k thermostat. Have old floor furnace. On old thermostat had two unmarked wires (a black and red). I connected the red to R and black to W, but it did not work. So then I connected the black to the Y and the heater kicked in. Problem now is it is always on, cannot get it to shut off, even when I move the setting all the way down. Is there something i am doing wrong or is the thermostat defective??

dac122

If you check continuity between R and W with the switch on heat and it doesn't behave right, you got a bad tstat. Same goes for R and Y in cooling mode.

SKIP4661

The Y is for cooling. I don't think it's an option on floor furnaces. I think the problem is the new thermostat is a 24 volt thermostat. Typically floor furnaces have millivolt systems which is very low dc voltage. It won't power a 24v thermostat. They do make digital thermostats that are compatible with millivolt systems. Will specify this on the package, usually powered by batteries.