I find it hard to believe that a HX on a 80% Carrier goes out in 10-11 y?
never seen one installed improperly? Or the filters only get changed when the limit gets replaced? 11 yrs is a lot of abuse, not saying the OP doesn't take care of it, just one of the many reasons for premature failure. But I wouldn't replace a heat exchanger on ANY 11yr old furnace, all the other parts are too old to expect them to last long enough to justify the cost, not sure what everyone else charges for the HX replacement, but our price would make me go with a new furnace.
Why the heck aren't furnaces designed so triggering a limit switch lights a big red fault light somewhere that the homeowner can see? Sort of like the equivalent of a car's "check engine" light. Many times a homeowner doesn't even know this is happening.
Case in point: me.
I learned about the problem my 80% Heil was having because I heard the limit switch cycling from the bedroom (due to an acoustic trick in the venting) one day while the furnace was in morning recovery mode. Turned out there were two metal "pre filters" for the original Honeywell electrostatic behind the filter. The original homeowner had deactivated the POS electrostatic and replaced the electrostatic elements themselves with a pleated equivalent but had left the pre-filters in place.
I diligently replace my furnace filter and was surprised as hell to hear the furnace cycling on the limit switch. Imagine my further surprise when I inspected behind the filter and found the 2 fully clogged pre-filters (now removed).
So now I've wired in a relay based sensor circuit that detects limit switch cycling (voltage to "R" drops when the limit switch activates on my Heil) and lights that big red light on my VisionPro 8000 TStat. The light can only be extinguished by power cycling the furnace.
All furnaces should have easily visable "Check Engine" lights IMO. You guys would do more business. Homeowners would be safer.
All furnaces should have easily visable "Check Engine" lights IMO. You guys would do more business. Homeowners would be safer.[/QUOTE]
All newer furnaces will go into a "hard lockout" requiring the power to be cycled to reset the high limit fault code. This fault code can be read through the front panel(some easier than others) via the LED on the control.