Okay, so my furnace is fairly new (just over a year), and we had this problem for a short time when it was first installed but thought we'd fixed it. The issue is that the furnace will come on, will be blowing hot air (or cold, during the summer), but will go off after 90sec. It will come right back on and start blowing the cooled or heated air again. It will go through this cycle about 6 times, then it will stay on until desired temp is reached. I should mention that the furnace doesn't actually seem to go off all the way - it sounds like it does, but it doesn't go through the same fan-blow then furnace turn on after the first cycle; sounds like it goes off, but w/in 8 sec comes back on full force. We changed the thermostat last summer, and that seemed to help the problem for a couple of weeks. We then tried using a std filter instead of the electrically charged one the installer put in, and that seemed to cure the problem. Lately our region has had temperatures in the teens and lower, and the furnace has started short-cycling again. Have tried changing the filter, or taking the filter out entirely; tried turning the thermostat down, and reducing airflow around the thermostat; tried calling installer, but he is unable to come out for a while. Oh, and now the furnace has started running until the heat is 3-5 degrees over what it's set on. I don't want my furnace to burn out, and can't afford to have whomever come in and "diagnose" for a fee. Any solutions?

Hopeful, you don't say the type of furnace, but if you look to the right side of this page, short cycling of furnace questions has been answered. Good luck