The draft inducer on my furnace sometimes starts and stops before the burner and blower finally go. Other times the furnace works perfectly normal. This is a Lennox 193UHE. It's only a couple months old and in a new house. No other exhausts on the furnace pipe. I have replaced the honeywell thermostat with a nest but the problem was there before the switch. I have changed the thermostat recently but the problem was there before that change.