I just bought a house with a daylight basement with 3 heaters in one room one of them being about 6-8 feet long and it will not shut off for some reason. This heater heats up the whole house even with the thermostat down to 50 and the other 2 are off completely. Any suggestions as to why this would happen? My guess is that it has to do with the thermostat but that does not explain why the other 2 heaters attatched to the same thermostat are working properly.

Sounds like the cable from the stat to this heater is spliced to the thermosat feed, rather than the load side of the stat.