I have a 20+ year old Coleman furnace with AC. The White Rogers thermostat has four wires connected, RC, W, G, Y. There in no jumber from RC to RH. There is a blue wire embeded in the wall but is not connected on either end. The AC worked great in hot weather. The problem now is that when the pilot light was lit and the manual switch turned on the gas valve activates and the furnace fires up and then the limit allows the blower to come on. The furnace runs smooth and heats very well, but it cannot be shut off from the thermostat. I have to kill the power at the switch or the breaker. The gas valve has a red wire running from the thermostat and a white wire from the thermostat. These wires have 24 volts continuously regardless of the thermostat. The valve is obvioulsy hot wired and wired incorrectly. There is no circuit board on this Coleman in the attic. It has a 24 volt transformer with 3 amp fuze and blower relay.

The gas valve should have a white wire from the thermostat and a blue wire from the transformer. The white wire should be connected to the red wire from the transformer at the thermostat when it is calling for heat. Most of the thermostats need the RC and RH both connected to the red wire. Some also need a B or C terminal connected to the other side of the transformer by the blue wire. Connect things up this way, and if it doesn't work, post back. A week ago, there were several similar questions with a honeywell thermostat. I couldn't figure out the problem. The thermostats can also malfunction if the batteries are low.