Stop the next steps will differ depending on which thermostat you are installing for single pole thermostats.
How to install a double pole wall mount thermostat.
Make sure to connect the ground to the thermostat or wiring box if available.
Two of these are live wires and two are load wires.
In my experience the wall mounted unit will control the temperature if placed in the appropriate location.
Since you are working with a double pole thermostat there should be four wires.
Thomas with cadet tech support shows you how to install a double pole wall thermostat on a 240 volt electric baseboard heater.
Typically this is marked l1 or line step 8.
You should be able to bypass the unit thermostat and utilize the wall mounted thermostat only.
Double pole 22 amp 120 volt 240 volt wall mount mechanical non programmable thermostat in white designed to replace most wall mounted line voltage thermostats 4 wire thermostat with color coded wires for easy installation.
It is usually attached to the wall and then with wire nuts to the wires coming from inside the wall.
Using a wire connector connect the hot supply wire to the thermostat wires.
Check out our voltage blog pos.