My keeprite DC90 NTG keeps blowing cold air

Problems related to residential installations.

My keeprite DC90 NTG keeps blowing cold air

Postby sunnyday » Wed Nov 14, 2012 9:34 am

Hello. I have a 12 year old Keeprite DC90 hi-efficency gas furnace. Starting about year 4, it would shut off suddenly, and the blower would continue to blow cold air. The repair guy came and could not find anything, and showed us the little "reset button" on the rollout to push if this happens. The furnace went on its merry way and did it twice that winter season. However, it was uncertain when it would do it, and luckily, up until year 7, we were home soon enough to push the reset button. Sometimes we would go away for the weekend and that side of the house (large house, two keeprites) would be frigid. Year 8 the pipes froze and we then burst and we had damage in the basement. Another trip by the repairguy found nothing wrong, although we complained and complained. We learned that we had to open up all the doors in our house and run the other furnace higher than normal in case the faulty one crashed. Last winter we had to have the blower motor replaced for $800. It still would shut off once a month at least. This year starting up the furnace it will only ignite and run for 20 minutes at most, and then shut off. The other Keeprite has never done this. Service guy come out, could not find any problem. He checked the heat exchanger visually but no holes seen. Used flue gas analyzer to try to detect Co2 in supply duct and cannot detect any. Verified 3.5" manifold gas pressure at main burner. Moved blower and venter and checked for obstructions. He could not find any other issues; however he recommended a brand new furnace ($5000 with installation) as he believes the integrity of the heat exchanger IS faulty, as there is a slight variation in the one of the burner's shape and slightly being pushed backwards when the blower is energized.
This is only a 12 year old furnace! Help! They also tell me that the rules in Ontario or Canada have changed now and the direct vent pipe, which exits to the front of my house, but makes a short jag to the left to exit next to where the other furnace vents, must now go straight out with no turns (I guess up into the ceiling and down again is ok?) so now I will have TWO ridiculous places where smoke steams out of the front of my house and kills any evergreen plants (I wasn't happy about it going out the front in the first place but we have a covered porch in the back yard. If I had known this issue in the beginnning, I could have had the furnaces placed in a better location).
sunnyday
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- My keeprite DC90 NTG keeps blowing cold air

Postby Freon » Wed Nov 14, 2012 2:55 pm

You said,"..* for 20 minutes at most, and then shut off." When the furnace shuts off, is the temperature at the thermostat the same as the temperature you have set the thermostat at? In other words, is the furnace shutting off because the house is warm enough according to the thermostat?

If not, when the furnace shuts off after 20 minutes, does the blower (main house air circulation) keep running? If so, for how long?

If the blower keeps running after the 20 minute burner cycle and does not stop, go to the furnace and see if the furnace tries to re-light? You will need to observe any re-light attempt within a minute of the burners going off, after running for the initial 20 minutes.
Freon
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