[kjonasson]

I have two baseboard heaters in the same room with one two-wire from the #2 heater to the main one. I have an external thermostat to the main heater... just one line. I hooked the heaters up but they don't seem to want to turn off. They are King ceramic baseboard. Is there a wiring diagram that shows this set up... I pulled some very old heaters out and wired the same but isn't working right. Also can you explain the value and differences of double pole and single pole?

[Missouri Bound]

The difference between single and double pole thermostats is not too complicated.
The single pole are usually used on 120v circuits where there is only 1 hot wire, and that is the one that is disconnected by the thermostat.
The double pole is used to disconnect BOTH hot wires in a 240V circuit.
I suspect you have wired it wrong and / or have used the wrong thermostat. There are connections for isolating one heater from the other or wiring them in tandem, as they were. Give a model number and we can look for the wiring setup.