Went out for no heat call and find roll out switch open for Lennox 90+ funace model# M/NG26Q3/4-100-5.Reset switch and look for anything what would cause this. Check out vent piping,gas pressure, induce motor,flame, filter everything ok .Get a callback it is out again .Only unusual thing observed was that right side of the burner box was much hotter then the left.First burner where is the igniter and roll out switch located is not alligned exactly with the flame chamber by manufacters.So I do not know if it is normal to get hotter on left side ori just the roll out switch is weak.Any reply is welome. thank you
A cracked heat exchanger can cause it...
Put your thermometer near the sensor while the unit is off and cycle it. Observe the temperature readings to see when it rises most rapidly. If it is noticeably after the blower kicks on then suspect the heat exchanger. If not then look elsewhere, such as perhaps a faulty IDB assembly, failing switch (can use blow dryer to check), or a combination of things such as a pressure switch out of adjustment + flue blockage (unlikely).
[Edited by sadlier on 10-24-2005 at 11:32 PM]
Can you look down from the top? That alignment don't seem right and you may need to pull the ht ex out to inspect. Not a big problem once you get things out of the way. Do flames change when blower comes on?