tempstar not heating to set temperature


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Old 12-19-09, 08:02 AM
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tempstar not heating to set temperature

Tempstar model #NUG5125BHB2

Seems to mostly happen in mornings, have programmable thermostat set to 68 but the it will only heat to 63 and then shuts off. If I turn the system off and let it start again it seems to heat a little higher, this time to 66. I have cleaned igniter and replaced thermostat. Is this some kind of limit problem?
 
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Old 12-19-09, 08:36 AM
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It very well could be a limit switch opening because the furnace is overheating.

I'd start by using a multimeter to check and see if the limit switch is opening when the burner shuts off.
 
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Old 12-19-09, 09:00 AM
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Is your air filter clean?
Did this problem occur before you replaced the stat?

http://icpindexing.mqgroup.com/docum...4108200100.pdf


 
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Old 12-19-09, 09:12 AM
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Filter clean, all vents open, other?

Yes filter clean, all vents open, cleaned all return vents. Will try leaving air filter door open tonight.

This just seems to happen in the morning, the rest of the day it runs fine. Could it be that night temp set too low(59) and then it has to run too much in the morning?
 
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Old 12-19-09, 09:22 AM
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Measure the temperature rise across the furnace with a digital themometer (available at Walmart for $10 in the kitchen area).

Compare the temperature rise to the rated rise that is listed on the furnace nomenclature. (usually @ 30 to 60 degree F. rise)
 
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Old 12-19-09, 09:57 AM
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Not heating enough

Your thermostat could be limiting the run time.
 
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Old 12-19-09, 03:06 PM
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Mark, there are some simple voltmeter tests per the already speculated possible problems, such as the high limit or stat shutting off. You can easily test to see if there is thru current. You may very rapidly find the problem by doing so, and end the mystery.
 
 

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