I wished I knew a more creative title for this post, but of the eight calls I had yesterday, this one was a PITA. The answering service called me and a talk to the tenant and the owner confirmed that something was clicking, the igniter was coming on. I thought it was the gas valve, because it was getting power and bouncing open and closed. Then the board started issuing a pressure switch error via the blinking light. What a mess. Then I remembered this was a Nordyne furnace and that the pressure switch was basically a call for heat on this design. After removing the Red and White wires from the board with the power off, place a jumper on the white and red terminals on same. Turn on the power to the furnace and if it starts up normally, the problem is in the thermostat. This is because when all the relays in the board are on, if the thermostat is weak, it will turn itself off and cause you to tear your scalp. Remember, before condemning the board, bypass the thermostat first if things are acting erratically. Don't forget to remove those wires first, or you'll cook the thermostat anyway. Also, I'm not picking on any particular product, but there are thermostat models that are cropping up every time I have one of these weird calls. There are more and these are usually consumer installed jobs, but the ones made mention of are usually professionally installed.