I have a Thermo Pride propane hot air furnace model CHA-100P with a White-Rodgers 50A50-113 Controller. After it is powered off, if you turn it on and try to fire it with the thermostat set well above ambient, it turns on for a second or two then dies. The light on the controller flashes six times. According to the manual six flashes indicates a “shorted flame probe or water level sensor”. I could not find any water level sensor terminals on the controller so I think it is safe to rule that out. That leaves the flame sensor probe. I checked between the probe and ground and found the resistance to be 468 k-ohms. My understanding is that the flame sensor circuit determines if the flame is present by the ionization of the gas in the flame. If that is the case I would expect the ionized gas to have a high resistance level so 468 Kohms might in fact be considered a short to the sensor circuit. Based on all this I have three questions.
1. Is 468k-ohms considered a short as I suspect and should the probe be replaced?
2. If the flame probe sensor should measure infinite resistance when disconnected from the controller, would it be a fair test to try to run the furnace with it disconnected. That controller would see infinite resistance in that case and I would think it would run at least until the time a flame should be detected. I would also think that would definitely be more than the 1 or 2 second it takes now to shutdown. I tried that and it still shuts down in 1 or 2 seconds.
3. Would there be any other reasons the furnace would shutdown in 1 to 2 seconds. All the other sensors test fine and are in the correct normally closed or open condition with no power.