Hi, I got 3 120 volt dimplex baseboard heaters running from a 2 pole 20-20 breaker on size 12/2 wure but on a 220volt 2 pole t-stat, but when I turn there t-stat to 70 degrees it trips the breaker,why? Can someone help

Are these 3 new 120volt baseboard heaters that you installed. If you put these on the existing 240 volt t stat and breaker it trips because your stat is set to turn the power on at 70 degrees. You need to have 240 volt heaters.

You need single pole thermostats for 120 volt heaters
Why do you have a 2 pole breaker? Should be a single pole also.

hi, i got 3 120 volt dimplex baseboard heaters running from a 2 pole 20-20 breaker on size 12/2 wure but on a 220volt 2 pole t-stat, but when i turn there t-stat to 70 degrees it trips the breaker,why? can someone helpReally? I hate to sound rude, but this is a classic case of not knowing what you are doing but doing it anyway.
WHY would you wire a 120v heater to a 2-pole 240v breaker??
Also, how is it wired? I bet you have a dead 240v short at the thermostat.

You have to tell us EXACTLY how each part of this is wired for us to even begin to help you. Even take pictures of everything and post them.

That said, my best advice is to get an electrician in there and correct the mistakes.