I have a lennox GX23 gas furnace. I have to turn the master power switch off and then on several times or turn the thermostat off and then back on to get the burner to fire and when it finally does fire, it only stays on for 3 to 5 minutes and then shuts off. It does not stay on long enough to bring the temp. In the house up to the thermostat temp. I then need to start the process all over agan to get the furnace to fire again.