Carrier 58CMA140-20 furnace Cycling as if Hitting Temp Limit


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Old 02-21-17, 06:25 PM
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Carrier 58CMA140-20 furnace Cycling as if Hitting Temp Limit

I stopped in at my folks home and their Carrier furnace was running for 15 seconds stopping for about 15 seconds, continuously doing this.
I took out the air filters and checked that the zone valves are open.

We had the system cleaned about a month ago and it is now on a service contract so they are on their way to check it but I'd like some opinions on this.
I'm thinking it could be the limit switch kicking in too early.

It has a Beckett AFG oil burner.

Thanks!
 
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Old 02-21-17, 07:01 PM
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Good guess but which limit switch.

It's hard to say what the problem is without making some tests but I doubt it's a limit switch. Since it's in 15 second increments it sounds like something wrong with the oil burner. Usually the burner will shut down in 15 seconds if it doesn't sense the proper flame.

It's supposed to shut down in 15 seconds not cycle.

Normally with an overheating problem.... the burner would run for several minutes and then shutdown for longer then 15 seconds.
 
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Old 02-21-17, 10:15 PM
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The tech pulled out the limit switch and ran it, it did exactly the same thing.
My theory is that the limit switch's resistance went up so that it heats just from the current to run the burner then shuts off. Basing this in the fact that it did the same thing in or out of the fire box. Tech jumped the switch and the burner kept on running so it needs a new one.
 
 

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