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Old 02-07-2015, 06:26 PM   #1
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Furnace overheating

I have a suburban sf 25 furnace that is overheating and throwing the limit switch which causes the burner to go off until it cools. It cycles on for about 2 minutes and on for 2 minutes. I replaced the limit switch, replaced regulator, checked amperage, made sure fan wheels are clear, all furnace outlets and hoses clear, and added two more vents to get more air out. Does anybody have any other suggestions? Thanks
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Old 02-07-2015, 06:31 PM   #2
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I am not an expert by any means but perhaps there is some type of blockage in your vents or furnace outputs..sorry reread your post and i see you checked for blockage
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Old 02-07-2015, 06:34 PM   #3
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Yep. Did Check for blockage. Thanks
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Old 02-07-2015, 06:57 PM   #4
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If you can not find any anything mechanically wrong with the furnace. Fan motor return air blocked floor dampers closed you my have a problem with the propane gas regulator supplying to much gas pressure. This condition will allow to much gas to enter the combustion heat ex changer causing it to overheat. You should have this serviced!!! If you are truly overheating the furnace you may destroy it instead of a simple fix.
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Old 02-07-2015, 07:02 PM   #5
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Quote:
Originally Posted by TimVWulp View Post
If you can not find any anything mechanically wrong with the furnace. Fan motor return air blocked floor dampers closed you my have a problem with the propane gas regulator supplying to much gas pressure. This condition will allow to much gas to enter the combustion heat ex changer causing it to overheat. You should have this serviced!!! If you are truly overheating the furnace you may destroy it instead of a simple fix.
X's 2 make sure you have enough R/A, also how many 4" ducts are attached to the furnace? You can also just have a bad limit. Put a little hole in the plenum and stick a thermometer inside a cooking one will work. see what temp it cuts out at and let me know. Do not touch any metal inside with the probe VERY IMPORTANT.
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Old 02-07-2015, 07:05 PM   #6
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Return air is clear, all the vents are open. I have 4 four inch vents and 2 two inch vents. I did have 3 four inch vents, but have added others trying to solve problem
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Old 02-07-2015, 07:07 PM   #7
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Also, heater was working fine up until this summer.
I did put in new regulator. I just took it to an rv mechanic who tested regulator and was the one who suggested extra venting
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Old 02-07-2015, 07:07 PM   #8
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Is the intake side clear?
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Old 02-07-2015, 07:09 PM   #9
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Yep. I took it out and pulled unit out of metal box to make sure
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Old 02-07-2015, 07:12 PM   #10
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I did replace the limit switch. Yesterday while mechanic was working on the unit, he had a heat gun type thermometer and it was cutting off at about 175
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