Trying to control a 220v radiant heater with a 24v thermostat. I have the transformer and it has a red and green wire on one side and a red and black on the other. I have it connected to the red and green. I lost the paperwork.
Anyway, it's not working.

Thanks

Green is usually ground, I would measure resistance and determine primary(a bunch of loops/coils of wire), and the secondary(aslo many windings of wire). Primary and secondary make no direct electrical connection) Does it have any screw terminals? Try to determine Primary, hook to 240 volts and see that you have 24 out of transformer.

What does the transformer do? Is this part of the original equipment that came with the heat kit?
A transformer just changes the voltage, it does not control or switch anything. You need a relay, not a transformer.

I bought is separately and hoped it would just turn off the heater when the temp was reached. If I need a relay, will I still need the transformer? Or is it all built in?
Thanks

A heating control relay will have the transformer built in.

You need something like this:
White Rodgers 24A01G-3 Electric Heat Relay

I appreciate your help. I'll look into it.
Take care

A "fan control center" usually has all the parts necesssary. A 24 V xformer and a contactor that surface mounts in a 4 x 4 electrical box. All you have to do is check the contact ratings.