Thanks HEATERMAN, awesome troubleshooting

[928tt]

Thanks HEATERMAN, your troubleshooting was right on the money !
I put a posting in a few days ago about my Keeprite furnace overheating and tripping the limit switch (flame rollout switch) in the burner box. The limit switch would trip not because of flame rollout, but once the furnace reached its set temp., the burners would shutoff, then the ventor motor would shutoff, thats when the rollout switch would trip. You said the problem was the HX. Once the combustion fan shuts down, the system blower is able to pressurize the HX and push enough left over heat and flue gases into the intake box, tripping the limit. The HX was checked and found that the round crimp rings that seal the 2 halves of each section together had broken off in several places. Looks like a bad design. Replacement HX same design, looks like I will be replacing HX again in another 10 years. Secondary HX also looks cheap, end caps are both plastic. Replaced HX and everything is fine again. Again thanks HEATERMAN for awesome troubleshouting!

[heaterman]

Your welcome. The HX was redesigned slightly but as you noted, it looks the same. From previous experience, I can tell you that it IS very much the same. They did away with the little washers but still use the same type of crimped eyelet. As far as the secondary goes, I have never had a bad one. The most important thing here is to keep the air filters as clean as possible. I would also hope that the repair contractor verified firing rate and temperature rise. Low air flow and or excessive temperatures are what cause most of the problems.

[Twilly]

Twilly knew HM was right on. Twilly says HM smart motor scooter.