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Old 11-10-2008, 06:03 AM   #1
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No heat from furnace.


Hello all. I have a Keeprite DC90 furnace that is 8-1/2 years old. I'm the original owner of the house and I've kept putting off having my ducts cleaned because of ongoing renovations. Last week I had my ducts cleaned for the first time and when the guy left, my furnace stopped giving off heat. The blower fan would keep running, even with the system set to off on the thermostat. A technician came out and reset the rollout switch on the combustion chamber, the blue flames sparked up and I got heat again. 10 minutes later I had to do another reset, and again about 20 minutes later until the house finally got warm enough and the thermostat stopped calling for heat (at this point the blower fan finally stopped running). This worked for about a week with no resetting until 2 days ago when I had to do another reset of the rollout switch, and now I have to keep resetting more often to get my house warm.
Is it possible that the rollout switch is faulty or is there a potential crack in my heat exchanger, as the technician said might be the case?
The company that did the duct cleaning swears they didn't touch the furnace but what a coicidence that it stopped working as soon as they left. They drilled 2 holes in the main heating duct a few feet above the furnace and I'm finding metal shavings everywhere - could some of these have fallen onto the primary or secondary heat exchanger and caused any problems?
Thanks.
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Old 11-10-2008, 06:23 AM   #2
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No heat from furnace.


I’d check the return air for blockage. Did you check the filter? Are the return air grilles un-obstructed? Air the supply vents open and unobstructed? These things usually don’t cause a roll-out switch to open, but what you are calling a roll-out switch may not be a true roll-out switch. Roll-outs are located on the shielding of the flame nozzles/venturi’s and sense for over-heat conditions in that area….usually caused by blocked exhaust venting or a cracked ht exchgr. Are there scorch marks in that area?
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Old 11-11-2008, 04:45 AM   #3
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No heat from furnace.


I don't see any scorch marks anywhere. There's no blockage on the return vents as the vents were just cleaned and I just washed the filters on my electronic air cleaner. As for the rollout switch, that's what the technician called it and the furnace schematic refers to it that way as well.
I don't know much about these things, I'm just scrambling for answers as to why this happened right after getting my ducts cleaned and how to fix it without having to rplace my whole furnace.
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Old 11-11-2008, 12:12 PM   #4
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No heat from furnace.


I’m not defending the duct cleaners, but things fail when they fail, and it always seems to come after someone touches an unrelated system. Murphy’s law, I guess.

I would suspect and consider having the heat exchanger inspected for cracks. I did some ‘Googling’ and seen some post of others talking about their Keeprite DC90 HX’s being cracked and rivets popped.

It’s been my experience that roll-out switches are pretty reliable, and few have manufacturing defects. That said, if a roll-out is shutting your furnace down, I’d say there is a strong chance something is causing it. Being very careful and keeping your face away from the burners, you can look to see if the flames ‘jump out’ towards the burner shield and roll-outs. When the furnace starts the flames burning and the blower is off, observe that the flames are going into the heat exchanger properly. If not, you can tell already that there is an obstruction in the HX or venting system. If they look good at that point, see what happens when the blower kicks on. A crack in the HX lets the air from the blower get in the HX and will cause the flames to react, depending on the amount of blower air that gets in. It may take a little while for the flames to ‘dance’ or roll-out. Depends on the size of the cracks and the expansion rate of the metal of the HX if there is any.

Think of the heat exchanger as being a tube that fire is shot into one end, and the exhaust is drawn out the other (to make the tube hot), and a blower blows air across the outside of the tube. The air blown across the outside is the air that heats your house. Since the fire is creating toxic gases, the air inside the tube should never mix with the air being blown around the outside of the tube. When there is a crack in the tube, the different airs are now allowed to mix, and depending on the exact physics at the moment, the blower air will be forced into the tube, suck the air out of the tube, or both.

I hope this helps.
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Old 11-11-2008, 10:05 PM   #5
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No heat from furnace.


good explanation sd515
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Old 11-05-2010, 10:41 AM   #6
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No heat from furnace.


Quote:
Originally Posted by sofakingwyld View Post
Hello all. I have a Keeprite DC90 furnace that is 8-1/2 years old. I'm the original owner of the house and I've kept putting off having my ducts cleaned because of ongoing renovations. Last week I had my ducts cleaned for the first time and when the guy left, my furnace stopped giving off heat. The blower fan would keep running, even with the system set to off on the thermostat. A technician came out and reset the rollout switch on the combustion chamber, the blue flames sparked up and I got heat again. 10 minutes later I had to do another reset, and again about 20 minutes later until the house finally got warm enough and the thermostat stopped calling for heat (at this point the blower fan finally stopped running). This worked for about a week with no resetting until 2 days ago when I had to do another reset of the rollout switch, and now I have to keep resetting more often to get my house warm.
Is it possible that the rollout switch is faulty or is there a potential crack in my heat exchanger, as the technician said might be the case?
The company that did the duct cleaning swears they didn't touch the furnace but what a coicidence that it stopped working as soon as they left. They drilled 2 holes in the main heating duct a few feet above the furnace and I'm finding metal shavings everywhere - could some of these have fallen onto the primary or secondary heat exchanger and caused any problems?
Thanks.
I have the exact same problem on my Heil DC-90...What did it turn out to be ??? cracked heat exchanger ? ring bad ??
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Old 11-05-2010, 10:43 AM   #7
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No heat from furnace.


I have the exact same problem on my Heil DC-90. WHat did it turn out to be ?? cracked Heat exchanger ??? bad ring ?
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Old 11-05-2010, 06:36 PM   #8
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No heat from furnace.


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Originally Posted by SD515 View Post
It may take a little while for the flames to ‘dance’ or roll-out. Depends on the size of the cracks and the expansion rate of the metal of the HX if there is any.

What would a dancing flame look like? I have six burners on my 20 year old Bryant LP condensing furnace. The one on the end farthest from the gas inlet doesn't seem quite as stable as the others. The flame is separating from the burner almost like it is being pulled away. Could that be an indication of a cracked HX?
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Old 11-05-2010, 09:16 PM   #9
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No heat from furnace.


Quote:
Originally Posted by artbuc View Post
What would a dancing flame look like? I have six burners on my 20 year old Bryant LP condensing furnace. The one on the end farthest from the gas inlet doesn't seem quite as stable as the others. The flame is separating from the burner almost like it is being pulled away. Could that be an indication of a cracked HX?
It very possibly could be. Or a plugged heat exchanger. Have you had it serviced lately?
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Old 11-06-2010, 04:56 AM   #10
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No heat from furnace.


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It very possibly could be. Or a plugged heat exchanger. Have you had it serviced lately?
Yes, my HVAC guy came out last winter to look at the flame and he didn't think it was a big deal but I am concerned.
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Old 11-06-2010, 06:24 AM   #11
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No heat from furnace.


If you haven't had the furnace looked at this year, I'd say it's due. The venturi might have rust/dirt blocking the gas from getting out, but 'dancing' flames that are being 'pulled' away from the nozzle are usually an indication of a problem with the heat exchanger.
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