First of all, I apologize for the long post....
I have a weatherking (not sure which model) which was installed in 1988 and it has ran flawlessly until about a week ago. My tenants told us they have been needing to reset the roll-out sensor every morning when they wake up. The furnace will run for approximately 12 hours before it trips again. Had the pro take a look at it - twice.
Pro tells me it is a heat exchanger without doing anything. Uses his CO sniffer on the vents in the house and it reads 4-5ppm from each vent after a lengthy warm-up period. He then sniffs near the bottom, left-hand side of the flue on the face of the furnace and it goes thru the roof. I ask him to scope the exchanger for me and he finds no cracks. He says it could be a flue blockage forcing the CO out of the front of the furnace. He doubts it is that though because the furnace and water heater share the flue and the water heater is not venting CO. I ask him to scope the flue. He does and finds no build-up. Ultimately, he ends up cleaning the pilot assembly and tells me everything is good.
Roll-out sensor had tripped again. This time he tells me it IS the heat exchanger. Says the flame is dancing a bit (which I would agree with). His boss comes over and quotes me a price for a new furnace.
Now to my questions...
Why does it take 12hrs for the roll-out sensor to trip?
What is the probability that the heat exchanger is the cause being that they have not shown me any cracks? My concern is that maybe the flue is partially blocked closer to the roof and even when the furnace is replaced, I will experience more problems.
Is there anything else I should have them check prior to installing a new furnace?
I have no problems replacing the furnace if it is bad, but I do have a problem fixing symptoms and not the real problem.
In the mean time, the tenants are on vacation and the furnace is off.
should have checked the flue draft if that is your concern, but a 23 y/o furnace is most likely cracked, especially that one. It may be that he simply missed a crack, or it is sooted up near the flue connection. 90%+ efficiency furnaces uses new pvc flues.....