Furnace thermocouple keeps going bad

Hi, I have a chronic problem with my home furnace. Too often, the pilot light goes out. Sometimes I can relight it, but after a few weeks, it becomes impossible to relight. If I change the thermocouple, it works fine for a few weeks, then the problem returns. What is causing the thermocouples to go bad? Thanks! Matt
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One thing that I have learned ( Family owns 25 rental units) is that these thermocouples can more often than not be recycled.
Try this next time: using a scotch brite pad, scuff the surface. Also, the blue tip of the flame (assuming it is a standing pilot) should be pointed at the mid section of the TC.
How old is the furnace?
larry
snipped-for-privacy@duke.edu (mdw7) wrote in

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Can you hold it up to the monitor? I can't quite picture that.
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Christopher a. Young
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Stormin Moron wrote:

<ahh...>
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Does the pilot give a good blue flame? Is the thermocouple in the flame?
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Joseph E. Meehan

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First. Sanding the thermocouple is a waste of time. IF the units in the flame good, the heats going to be transfered and will work. If its not covered in white ash, then sanding is a waste of time...did I say that sanding is a waste of time?
Second.
Thermocouples come in many qualitys...really. Honeywell is not always the best in this case...however, you are not going to get a quality TC for $5 at Lowes. The ones we sell are $25 wholesale and we get ZERO failures thus far.
Third.
Installation. If the units been dropped, or mangled and someones bent it at crazy angles to try to get it in place, its going to fail sooner, than later. Also, the flame for the unit does NOT need to cover the entire unit....just the tip....say..1/3 or less of the unit...any more, and its going to fail.
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This is Turtle.
Like CBHVAC said I think you have one of these two problems.
1) your buying cheap thermocouples at Home Cheap-0 and they are failing like they are suppose to.
2) Your heating up the middle to the bottom of the thermocouple head and it will burn it up. The flames should not hit nothing but the top 1/3 of the thermocouple head to work properly. If you heat the bottom half of the thermocouple head. you will get a negitive 24 mill-volts. If you heat the top half of the thermocouple head you will get a possitive 24 mill-volts. If you heat the middle of the thermocouple head. you will get a + positive 24 mill-volt and a negitive 24 mill-volts which equals zero mill-volts but then in about a week it will burn up completely.
So back to statement # 1 : heat only the top 1/3 of the thermocouple head and use a hvac thermocouples and not the hot water tank thermocouples. Home Cheap-0 does not sell hvac thermocouples and you will have to go to a hvac supply house or appliance parts house and get a hvac thermocouple [ used for gas hvac furnaces ] to use. The hvac thermocouple will run you $12.00 to $25.00 depending on length and brand. Hot water thermocouples put out about 26 mill-volts and a hvac thermocouple will put out about 30 mill-volts. A thermocouple can loose as much as 1/2 a mill-volt per year of operation and will last 8 years longer than a hot water tank thermocouple.
TURTLE
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