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Discussion Starter #1
Hello! Long time lurker here, however this is my first post.

Having an issue with my Carrier Furnace and was hoping someone would be able to provide some insight to the cause.
Sporadically during the overnight hours the past two weeks my heater has been shutting off. This only occurs during the overnight hours between midnight and 4am. The led is flashing error code 13, which translates into an error 33 "Limit Circuit Fault" code as per the owners manual. When the heater malfunctions/shuts off, it emits an odd odor throughout the house as well. Turning the power off and then back on seems to clear the code each time and allow it to run the rest of the day. Up until recently (last evening) the heater would function as normal until the overnight hours. Last evening I was able to observe more of what was happening: I noticed that the thermostat would call for heat even when it indicated the same room temperature as that where the heater was set for....room temp was 71 and heater was set to maintain 71....even then, it would call for heat (you can hear the "click"). The small induction motor comes on prior to the flame ignition, the flames ignited however the large blower motor did not turn on. I could then see the 13 led code flashing. A few moments later the flames/gas shut off and then the large blower motor came on and ran for several minutes. I'm not sure but the odor we're smelling might be that of the excessive heat coming off of the heat exchanger?

Ive checked the duct work - all open and no change since the installation of the heater and duct work (approximately 5 years ago). The filters are clean and I don't know of any obstructions. I will be checking the exhaust and fresh air intakes this afternoon for any blockages.

If anyone has any other suggestions or may have seen this before....any an all input would be greatly appreciated. I'll likely be calling a technician later today to look at the unit.

My apologies for such a long post, however I wanted to be as descriptive and thorough as possible.
 

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Discussion Starter #3
It seems odd that sporadically the blower motor does not come on or that it was so delayed....which I guess would cause a thermal shut down? I read about a possible cracked heat exchanger, which is very concerning, but then again, the odor is not there all of the time, and the flames are burning very well, blue with no yellow or blow back (not sure if that is what it is called).
 

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Your unit is not on the list of those affected by the class action lawsuit.
It appears you have an ECM motor in that furnace. Could have something to do with the module.
Do you have a meter? You’ll need to check some parts of the blower control.
Flame rollout is the term your looking for on the heat exchanger.
 

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Discussion Starter #5
Thank you very much. Yes I have a meter and should be able to check the blower control. I'll see if I can locate that on the schematic.
 

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this unit is newer and should be covered by parts warranty.
 

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Discussion Starter #8
That would be great if it is covered by a warranty! Right now the furnace seems to be operating fine. I'm relatively certain that tonight it will shut down again.

Since the blower seems to be working correctly at this time, is there any reason to check the module? Just thinking that it will show correct voltage/resistance? Cant thank everyone enough for your input. If you have any other ideas, please let me know. Trying to take care of this before we get into the teen's this weekend.
 

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Parts can be covered by warranty, labour won't be unless you have a specific plan for that u paid extra for.

When it fails, you have to see if the motor connections are getting proper voltage. Could be the board or the module.
 

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Discussion Starter #10
Ok, on the motor connections. I will try to check it if and when it fails to come on again. I finished checking both the exhaust and fresh air intakes for obstructions and they are both clear. If parts are the only thing covered, I'll take it. Anything covered under warranty would be better than nothing.
 

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you have to use a contractor to get the parts covered by warranty. may cost you over a couple hundred but the motor is very expensive if replacement is required.
 

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it will either have a 5 year warranty or a 10 if registered.
 

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Discussion Starter #14
Technician said the issue is most likely in the circuit board. They are replacing on Monday....guess we'll see. I'll provide an update when it is replaced. And as you guys mentioned, they told me parts are covered up until the 5yr mark. Thanks for that info!
 
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