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How do I know if furnace thermocouple is bad?



 
 
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  #11  
Old November 1st 06, 02:41 AM posted to alt.home.repair
mm
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Posts: 7,843
Default How do I know if furnace thermocouple is bad?

On Tue, 31 Oct 2006 17:02:27 GMT, "
wrote:

BTW, the furnace is an Amana Air Command 95. I have a digital
thermostat and replaced the batteries. No effect. No breakers are
thrown.


Is it gas, oil, or something else?
Ads
  #12  
Old November 1st 06, 02:47 AM posted to alt.home.repair
mm
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Posts: 7,843
Default How do I know if furnace thermocouple is bad?

On Tue, 31 Oct 2006 20:10:28 GMT, "
wrote:


Fuses rarely fail on their own, they are usually an indicator of a
problem elsewhere.


We had some warm weather over the weekend, so I turned the thermostat
off. I asked my son to turn it back on, and I noticed that the fan
switch was set to "On" instead of "Auto."

Would the blower running continuously for a day or two be reason
enough to blow the fuse?


Are we talking about a fuse in the main fuse box or somewhere else?

A fuse that is a glass cylinder 3/4" long and less than 1/4" in
diameter. Or one that screws into a socket almost as big as a
lightbulb socket?

What size failed? How many amps? What size have you been using since
you moved in. Replace the fuse with a 15 amp fuse, unless you know
for sure it was supposed to use bigger and had used bigger, and see
what happens.

  #13  
Old November 1st 06, 02:59 AM posted to alt.home.repair
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Posts: 6,757
Default How do I know if furnace thermocouple is bad?

mm wrote:

On Tue, 31 Oct 2006 20:10:28 GMT, "
wrote:


Fuses rarely fail on their own, they are usually an indicator of a
problem elsewhere.


We had some warm weather over the weekend, so I turned the thermostat
off. I asked my son to turn it back on, and I noticed that the fan
switch was set to "On" instead of "Auto."

Would the blower running continuously for a day or two be reason
enough to blow the fuse?


Are we talking about a fuse in the main fuse box or somewhere else?

A fuse that is a glass cylinder 3/4" long and less than 1/4" in
diameter. Or one that screws into a socket almost as big as a
lightbulb socket?

What size failed? How many amps? What size have you been using since
you moved in. Replace the fuse with a 15 amp fuse, unless you know
for sure it was supposed to use bigger and had used bigger, and see
what happens.


I'm assuming from the reference to circuit breakers earlier and then
this reference to a "buss fuse" that he means a small glass 3AG or 5x20
fuse in the thermostat itself possibly located when removing the
thermostat from the sub base to check for control power. It would help
if he posted more complete details though.

Pete C.
  #14  
Old November 1st 06, 03:04 PM posted to alt.home.repair
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Posts: 7
Default How do I know if furnace thermocouple is bad?

The fuse is a 25A "Edison base" fuse in the switchbox on the furnace
itself.

There's no reference to the fuse anywhere in the manual.

I've lived here for 7 years, so the fuse is at least that old. The
house is 12 years old.
  #15  
Old November 1st 06, 03:52 PM posted to alt.home.repair
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Posts: 6,757
Default How do I know if furnace thermocouple is bad?

" wrote:

The fuse is a 25A "Edison base" fuse in the switchbox on the furnace
itself.

There's no reference to the fuse anywhere in the manual.

I've lived here for 7 years, so the fuse is at least that old. The
house is 12 years old.


Sounds like the builder recycled an old fusible disconnect since they
haven't used edison base fuses for quite some time. New ones use
cartridge fuses, or they use small circuit breaker panels.

At any rate a problem might still exist since fuses usually blow as a
result of a problem, not old age. 25A is also a pretty large fuse and an
oddball size as well so it may not be the correct one, 20A or 30A would
be expected.

You haven't indicated what type of furnace this is yet (oil, gas, etc.)
but most would be expected to be on a 20A circuit since burners and
blowers don't take that much power. Possibly the blower bearing are
going or it's clogged up and is drawing more power than normal?

Possibly a pre-existing condition where someone overfused to 25A to mask
the problem? What size breaker is feeding the furnace from the main
panel? What gauge wire is feeding it if you can see? 12ga would be good
for 20A, 10ga for 30A.

Pete C.
  #16  
Old November 2nd 06, 03:49 AM posted to alt.home.repair
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Posts: 165
Default How do I know if furnace thermocouple is bad?

FWIW, the function of a thermocouple is to keep the safety portion of
the gas valve open on systems with standing pilots. Does your unit have
a pilot? There were some units that were available with standing pilots
12 years ago, but they were already getting pretty rare even then. If
you do not have a pilot, I kinda doubt they replaced the thermocouple.
Larry

  #17  
Old November 2nd 06, 04:28 AM posted to alt.home.repair
mm
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Posts: 7,843
Default How do I know if furnace thermocouple is bad?

On Wed, 01 Nov 2006 14:52:57 GMT, "Pete C."
wrote:

" wrote:

The fuse is a 25A "Edison base" fuse in the switchbox on the furnace
itself.

There's no reference to the fuse anywhere in the manual.

I've lived here for 7 years, so the fuse is at least that old. The
house is 12 years old.


So did you replace it, like I said to? What happened?

Sounds like the builder recycled an old fusible disconnect since they
haven't used edison base fuses for quite some time. New ones use
cartridge fuses, or they use small circuit breaker panels.

At any rate a problem might still exist since fuses usually blow as a
result of a problem, not old age. 25A is also a pretty large fuse and an
oddball size as well so it may not be the correct one, 20A or 30A would
be expected.


This is the wire going TO the furnace, right? I recently learned in a
thread here that the wire IN the appliance might have better
insulation and maybe doesnt' have to be as thick a gauge as the wire
from the main box to the appliance.

25 is unusual, and I too would be very reluctant to go to 30. But if
he has been using 25 for 7 years, I'd find myself some 25s. If it
normally uses 22 and once used 27 and blew the fuse, he'll never find
why it once used 27. If it blows the new one, then he may have /
probably has a findable problem.

Of course I agree that a blown fuse represents a bigger problem at
least half the time. Similar to this, a couple days ago, my hot
water limit switch tripped, and I reset it by turning off the breaker,
taking off the cover, pushing the red button, and turning the breaker
on again. It tripped again not long afterwards (don't know when.)

OTOH, in the trash I found a Black and Decker air pump (they call it),
and on the cigarette lighter plug, it said "No user serviceable parts
inside", but they lied. Inside was a glass fuse, and after I drilled
out the rivet, replaced the fuse, and somehow put the plug back
together, the pump has worked fine for a long time. I wonder why it
blew.
You haven't indicated what type of furnace this is yet (oil, gas, etc.)
but most would be expected to be on a 20A circuit since burners and
blowers don't take that much power. Possibly the blower bearing are
going or it's clogged up and is drawing more power than normal?

Possibly a pre-existing condition where someone overfused to 25A to mask
the problem? What size breaker is feeding the furnace from the main
panel? What gauge wire is feeding it if you can see? 12ga would be good
for 20A, 10ga for 30A.

Pete C.


 




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