Sorry it took so long to reply but i just saw this thread again....
No Jim it should not be a bandaid. Its a component of the furnace just like a battery for a bike. replace it and you should be okay to run again.
Its hard for me to believe your furnace is only 7 years old and this many problems. As far as air flow goes the contractor should have taken square and cubic feet to calculate the amount of cfm needed to provide adequate HVAC.
The only thing that makes me nervous about your original post is the fact you said "purge". Are you 100% positive you have a purge cycle? Usually that is typical of boilers and you are talking natural gas forced air furnace right? Where the gas turns on and you see the flames going up into the exchanger right? These are answers that must be 100% answered correctly.
I am assuming you do mean forced air, natural gas, furnace with an "a" coil for AC right?
Okay time to diagnose your air flow situation. What color is the big flames when the furnace kicks on? This is important. Nest is your hot water heater gas as well? Does the gas vent on your water heater tie into the same flue on your furnace? if so there should be a gap of approx. 2" at the top of the water heater. take a match and light it; place it close to the opening on the top of the heater (flue) and just lightly blow it out and the smoke should travel up or be pulled up the vent. if so you have good vacuum to remove the expelled dioxide. (that is VERY important) if it dose not seem to get pulled up the vent you could always take a leave blower on low and stick it into the end and force air through to clean out any blockage. (it would be rare for this to get blocked) BTW if it were totally blocked for the last couple winters you would not be here so lets assume
you said all 3 returns are open (you should not be able to close these) and not blocked. Turn your fan on/auto switch (TSTAT) to on. Do the same trick with the match to each return. smoke should get pulled in. Now ensure most all of your discharge vents are open and blowing air. Sometimes a damper can get stuck in the duct work and close off an entire section of the home.
Just like a car. Air in; air out. Too much air in and not enough air out will be bad. you know what i am saying right?
okay this is a good test to (without a cfm hood) test cyclic. place a new air freshener or something that gives off a distinct odor (not your ass either!
) by one of the returns and then with the fan running obviously go to the discharge and see if the smell is pulled through and pushed out.
Do you change your filters often? Do you have an air flow switch? What that does is proves the fan is blowing air. Sometimes these get dirty. (Rarely but sometimes)
If all seems fine and all my assumptions are correct and the fan when in heat comes on shuts off and so on even when the flames are not visible and enough time has gone by to warrant a shutdown then yes i would stick to my original guess of a bad Fan limit control switch. Like i said earlier it works on rise and fall of temperature and it is also adjustible so make sure no one "played"with the temp related on/off time.
Good luck and sorry for HVAC 101 book