We have a brand new Tempstar T9MPV gas furnace and Heat Recovery Ventilator, which both have separate but somehow linked Thermostats. Our furnace blower cycles between High and Low for less than 30 seconds at a time and the burner stays on for about the same time. Filters are kept clean. What could be causing this cycling? Since I originally posed this question the front of the blower and the front of the gas burner chamber were opened. Somehow the blower got reset and it quit short cycling. We also replaced the one month old intake air filter, which was bowed a bit. Did we inadvertently reset something?