I have a four wire bundle going from gas furnace to thermostat with only two connected. Red to RH and green to W. I just had a new furnace installed and the installer tried wiring the white wire from furnace to thermostat but furnace wouldn't run. I want to add a new thermostat that needs all four wires. I checked continuity of white wire and it checks out as being good but when I switch out the green wire and replace it with the white wire something kicks on in the furnace even though I have the thermostat set below the current temperature. A motor runs but the furnace doesn't come on and heat. What might be the problem here? Thanks for any thoughts. Peter.

I have a furnace, a Tempstar NTC5150 BKC1 which runs (lights up the gas burners) for about 2 minutes and 20 seconds. The gas burners shut down. The small exaust fan runs on and on. The furnace seems in OK shape. That is no rust or physical damage. I have in the last few years replaced the control board, the gas valve and a few of the thermocouple igniters, just now trying a new one also. The limit switches seem to function. The vacuum switch seems to be working. New clean filter, and the flu is shared with the water heater, and that is working fine. There are no leds on the board. Any ideas?