Hi maybe someone can make a suggestion for me. I have a noma programmable thermostat and a lennox energy efficient furnace with central air. Twice now my furnace has stopped blowing hot air but continues to blow cold air. When I take off the air filter cover for about a minute and put it back on the funace stops blowing the cold air, ignites the burners and starts blowing hot air again. I had replaced the air filter before it last stopped working. Any suggestions would be appreciated, thanks Allanminor