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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 21934
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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My Tempstar furnace will start blowing cold air, the re-set

Customer Question

My Tempstar furnace will start blowing cold air, the re-set (re-coil) button located on the side of the heat exchanger box will have to be pushed. This has happened periodially the last year or so...however, increasing to 3 or 4 times this just this fall. One service repairman (after 3 previous visits, no inspection of furnace, just pushing re-coil button) said I had a cracked heat exchanger by measuring the outside exhaust (1400PPM Carbon Dioxide) ONLY!!! No check of air quality inside at all, or even looking at furnace. So I called another technican who could not confirm cracked air exchanger, drilled hole in duct on top of furnace and measured between 0 and 1 ppm of CO, and O reading when on a main floor register. I have 3 CO detectors in my house, no alarms from them. So.....could there be some other problem?
Submitted: 6 years ago.
Category: HVAC
Expert:  BillyHvac replied 6 years ago.

IF the vent CO was 1400ppm, you have a crack or very very dirty burner. The end result is if the rollout sitch is tripping it means the flame is not getting through the heat exchanger as designed.


There are only 2 reasons why....exchanger is cracked or plugged. Either one requires a lot of work.


Being that particular brand and model the odds are that the heat exchanger is indeed cracked. There are pressed rings at compressed sections of the exchanger that popped and cracks originated there.


A good burning furnace is under 100ppm if you take a reading before the circulation blower cuts on it is lower and then climbs after blower start up.


With my experience with this unit and the symptoms do have a racked exchanger.

Customer: replied 6 years ago.
I was first told (by a private business that sells furnaces) that the heat exchanger was cracked on 3/08, then told by a Natural Gas Technican that it wasn't. Now the private individual (another business) says they can't confirm it, and the gas company technican says yes. So could my furnace have ran for almost 2 years with a cracked exchanger? And why are no alarms going off? This furnace was put in in 1998, so it isn' too old. And supposedly has a 20 year warranty. Also, this furnace was installed in a new house that wan't finished at all; we have been doing all the construction work here sheetrocking, painting, cutting tongue and groove wood, etc. etc....
Expert:  BillyHvac replied 6 years ago.

Just because there is a crack does not mean CO in house or possible sickness or death. Look at a is a heat exchanger missing an entire side, but there is no danger as long as it drafts. The draft fan is pulling the c.o. through and out.


The only really dangerous furnace was a Lennox Pulse because it ran with a pressureized heat exchanger and it could force CO through any cracks.


Most Tempstar, Heil, Intertherm (all ICP Products) had this issue. It is just when the crack gets large enough that the blower gets into the exchanger and pushes flame.


As long as the CO gets outside your detector will not go off. Also it has to do with clean burn. What is a gas stove or oven? No chimney pipe and burning detector goes off.....Because it burns clean with minmal CO.

Customer: replied 6 years ago.
I still feel that there needs to be more investigation into this matter. I was told it was cracked last year, then told it wasn't .This year a the same party that said there was no crack last year is saying it it cracked , while another contractor is saying they can't confirm it. And as I mentioned before, they didn't even examine the furnace, just took the CO reading outside. And they came here 2X previously this fall for same symptom (blowing cold air) and never examined the heat exchanger or even mentioned it, just reset the switch. So I don't feel I should just go buy another furnace on that...... Shouldn't they have (at least) taken the front off the heat exchanger and examined the flame? Do I just have to take their word for it as they red-tagged it? Does their opinion take presidence over the other opinion? The last party did mention that my furnace may be oversized for my house (125,000 btu for a 45'x28' home with full basement and loft, basically 2 stories as the living area is cathedral) As this heat exchanager is only 11 years old and warranty is for 20, will Tempstar go good for it? If not, what furnace would you recommend? Should I try having someone clean this furnace before going any further with this cracked heat exchanger diagnosis?
Expert:  BillyHvac replied 6 years ago.

I know this furnace well.


I know the odds are very very high that if it does not have a ringlet crack it will.


I know you are in a quandry of it is cracked or not...but that is what this furnace was known for. If the exhaust showed that high of CO and being on a Tempstart NUGM, it is certain you have a crack.


If you would like to pay a company to disassemble the unit and show you the cracks, I understand. But I have taken these apart, I have replaced the heat exchangers and I do know the historty of this unit. In my opinion if you pay anymore money to inspect you are wasting time and money.


The heat exchanger will be replaced with the parts free but labor not.


100,000 btu would be better suited for your home.

Customer: replied 6 years ago.
Ok, I guess I had better resign myself... I just find it hard to accept with conflicting results. So.... what furnace do you recommend? I have a quote for a Bryant with a 10 year warranty, and will be getting one for a Comfort Zone? The only other business in town sells Trane. you have any ideas for how I can contact Tempstar? The number on my warranty info. is out of service???
Expert:  BillyHvac replied 6 years ago.

The Bryant and Trane are both great choices with convenient numerous contractors.


Here is a link for you to find a Tempstar dealer for assistance.


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