Furance Starts up and runs for Approx 15 minutes then shuts off before reaching the thermostst temperature setting. After the furance shuts off I can restart it, but each time the furance runs, it runs for a shorter time. I know it's not the thermostat and it has an electronic ignition. Does this furance have a high limit temperature sensor that may be bad? If it does have this sensor, where is it located?
