I have a room which has three baseboard heaters controlled by one thermostat. Two of the smaller heaters did not warm at all. The remaining one heater ( the largest) is always on. The fuses were removed ( one side was extremely hot) and the heater cooled down. The thermostat single pole was replaced and all three worked properly until the day after when the large heater again stayed on but the two smaller ones worked fine. Help...

You have a electrical problem. Take a meter and check all legs for proper voltage. Next take a AmpProbe and check the current draw. Sounds like a intermittent short or to high a current draw. Defective thermostat can also cause this problem.