I have a steam heating system, with 6 radiators on it. The thermostat is set to 75 degrees. The radiators in the living room (where the thermostat is located), the dining room and a bedroom are all warm, and the room temperature is 70 degrees. The other three radiators are ice cold. Everything seemed to have been working fine, until the utility company came a replaced the thermo coupler. What could the problem be?