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?
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?
firstname.lastname@example.org (mdw7) wrote in
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?
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
The ones we sell are $25 wholesale and we get ZERO failures thus far.
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.
wrong! wrong! wrong! i just did it. works fine. friday 3:30pm 2/24/17 . tried
lighting pilot for an hour. nothing. could not get pilot assembly until monday.
pulled burner assembly. slight carbon build up on thermocouple. used 440 grit on
tip of thermocouple . replaced assembly. has been working fine ever since. it is
now 4/28/17. got the part now for when it does fail again.
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.
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