Our old thermostat for the heater has 2 wires only. They are both black. The new thermostats have 3 or more colored wires. What should we buy to replace our now broken thermostat that is easy to install without calling an electrician to change the wiring?:eek:

For heat only, just connect one black wire to the R or RH terminal and the other to the W. Might be better if you identified the hot and connected it to the R, but not that important.