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

If that Lennox has a cam stat fan/limit control that is probably the problem just my best guess.

When it happens again, look on the circuit board through a small viewing port. You should see a blinking light. This is a diagnostic code that will stear you to the area of the issue. On the backside of the access panel, you will find a diagnostic code chart. I dought it's your filter, just every time you open up the furnace, you are reseting the control.