Resistance of thermal switch in thermocouple - does it matte

[Danny D.]

Does the difference in resistance matter if you replace a 24-inch 30mv
thermocouple that has a thermal switch versus one without the thermal
switch?
http://i.cubeupload.com/xqThcA.jpg

I bought a generic Honeywell 30mv 24-inch thermocuple (PN CQ100A1013) from
Ace Hardware:
http://www.acehardware.com/product/index.jsp?productId=11877505

That picture in the URL above is wrong because it's 24 inches:
https://www.amazon.com/Honeywell-CQ100A1013-Replacement-Thermocouple-Furnaces/dp/B000BPHNW2#productDetails

When I went to put it in the hot water heater, I belatedly realized the
original thermocouple has an integral thermal switch.
http://i.cubeupload.com/TtyF4c.jpg

I know the length matters, from a resistance standpoint, but the hardware
store owner had never heard of a thermocouple with at thermal switch
before:
http://i.cubeupload.com/z1862F.jpg

The thermal switch is a safety feature that will shut down the pilot if the
heat under the hot water heater gets too great:
http://i.cubeupload.com/Qh4PMI.jpg

When I call Sears in San Jose at 408-274-2593, they confirm the part number
is PN 9000056015 but that replacement part doesn't seem to have a thermal
switch on it.
http://www.supplyhouse.com/AO-Smith-9000056015-Thermocouple-Kit-Model-TC-K24
https://www.heritageparts.com/Napa-Technology/Manufacturers/A-O-Smith/A-O-SMITH-THERMOCOUPLE/p/AOS9000056015
http://www.jupiterheating.com/ao-smith/parts/9000056015.html
http://www.terapeak.com/worth/new-state-a-o-smith-9000056015-thermocouple-kit-model-tc-k24/230984311909/

Have you ever had to make the decision of whether to replace a thermocouple
that had a built-in thermal switch with a generic thermocouple that had no
thermal switch? Did the resistance match?
http://i.cubeupload.com/nFG8Ip.jpg

 

[Danny D.]

On Fri, 19 Aug 2016 16:33:50 -0700 (PDT), trader_4 wrote:

I'd say the resistance doesn't matter because there probably is no
material difference in resistance. But without the thermal fuse,
whatever safety that it provides is gone. In other words, it should
work, but without the additional feature. Does it? I guess the
question comes down to is what you wind up with the same as my WH
and most others that don't have this or does my WH and others have
some other way of thermal cut off instead that yours doesn't have,
thereby leaving yours unsafe? IDK

IDK either.

The book resistance of the Honeywell CQ100A1013 thermocouple is apparently
0.2 ohms but that's all I could find out by way of technical specs from
either Sears or from Honeywell.

Sears confirmed the replacement part number is 9000056015, but when I look
up *that* part number, none of the pictures show the thermal switch.

The fit of the Honeywell CQ100A1013 "universal" thermocouple isn't even
close to the same as the original fit either as the mounting for the
original is screwed on with a plate while the "universal" Honeywell
thermocouple is a screw on nut which doesn't have a corresponding mating
female.

Therefore, the "universal" thermocouple isn't even close to universal,
although I can probably bend some metal to make it fit - I'm basically
making my own parts out of raw materials.

When I called Honeywell technical support at 800-468-1502x1x1x9x1 to find
out if they have a closer replacement than the Honeywell CQ100A1013 that I
bought, they drove me nuts in so much as they don't even understand the
simplest thing about the product they sell.

All they could tell me is that it has to go 1/2 inch into the flame.

When I asked for a thermocouople with a theroswitch, they told me to use
the Q340A1074 but that doesn't seem to have a thermoswitch either.
https://www.amazon.com/Honeywell-Q340A1074-International-Thermocouple/dp/B00E0CWKPC

So I'm basically making my own parts from raw materials because the mounts
aren't even close on *any* of these so-called replacement thermocouples.

 

[Danny D.]

On Sat, 20 Aug 2016 01:21:37 +0000 (UTC), Danny D. wrote:

So I'm basically making my own parts from raw materials because the mounts
aren't even close on *any* of these so-called replacement thermocouples.

I concluded the "universal" mount stood zero chance of fitting.
http://i.cubeupload.com/mYJNjq.jpg

There is just no way a "universal" thermocouple is going to stay put there.
http://i.cubeupload.com/8G0mAF.jpg

Just look at this bracket for my original thermocouple.
http://i.cubeupload.com/vQVXGL.jpg

For now, I sandpapered the thermocouple and put it back in, but I think
I'll either have to find an exact replacement or build my own bracket
assembly.

I can't believe everyone runs into this fit problem.
Do you?

 

[pfjw@aol.com]

Nomenclature is your problem here.

a) A THERMOCOUPLE is a bi-metallic device that generates small amounts of electricity when heated.

b) A THERMAL SWITCH is a device, typically filled with mercury or some similar material that when heated to a specific temperature - or higher - closes a switch by expansion. From 3', you would not be able to tell one from another.

THEY ARE NOT INTERCHANGEABLE. Full Stop.

c) A THERMAL FUSE such as the one you picture is also a bimetallic device that opens at a specific temperature. Some such devices will reset, some will not. Most will cycle only a few times before they fail altogether.

You will have to purchase THAT and ONLY THAT part for replacement. Call the manufacturer of your heater and get the part number. Local suppliers such as Ferguson may have them, or any good plumbing supply house. This is very unlikely to be a Home Depot or Ace Hardware device.

Do yourself and your family a favor and don't spend 10 days trying to kluge something stupid that either won't work, be dangerous or worse. Save your gas, their sanity and their time. Just get *THE* *RIGHT* *PART* the first time.

NOTE: If the water heater is more than 10 years old, replace it. It will be done anyway shortly and you may as well do it now. Given that the replacement is $143.00, think hard before buying a part over a new unit.

Peter Wieck
Melrose Park, PA

 

[pfjw@aol.com]

Just to be clear - as you often need a clue-stick applied repeatedly to clear the blather:

a) A THERMOCOUPLE operates by holding a magnetic pilot light valve open by generating small amounts of electricity. If the pilot fails, the electricity stops and the valve closes.

b) A THERMAL SWITCH holds an electrical switch closed by pressure.

c) A THERMAL FUSE opens at a specific temperature.

Do you even know which part has failed?
Are you even contemplating bypassing the thermal fuse? Do you care that little for your family?

Peter Wieck
Melrose Park, PA

 

[Retired]

On 8/20/16 12:13 AM, Danny D. wrote:

On Sat, 20 Aug 2016 01:21:37 +0000 (UTC), Danny D. wrote:

So I'm basically making my own parts from raw materials because the mounts
aren't even close on *any* of these so-called replacement thermocouples.

I concluded the "universal" mount stood zero chance of fitting.
http://i.cubeupload.com/mYJNjq.jpg

There is just no way a "universal" thermocouple is going to stay put there.
http://i.cubeupload.com/8G0mAF.jpg

Just look at this bracket for my original thermocouple.
http://i.cubeupload.com/vQVXGL.jpg

For now, I sandpapered the thermocouple and put it back in, but I think
I'll either have to find an exact replacement or build my own bracket
assembly.

I can't believe everyone runs into this fit problem.
Do you?

According to this A O Smith webpage, see page 18 at
http://www.hotwater.com/lit/training/320991-000.pdf

"the thermocouple is not a separate replaceable part."

"There is no routine service associated with the TCO"

"The TCO is an integral part of the thermocouple and
not replaceable as a separate item. A pilot burner assembly must be
reinstalled."

See picture and instructions on page 20

Not knowing your specific model & serial numbers, 2 possible parts are
shown at
https://www.wallingfordsales.com/products.asp?cat=564&pg=68
P/N's 9006013005 or 9006014005

 

[Danny D.]

On Sat, 20 Aug 2016 08:24:06 -0400, Retired wrote:

ccording to this A O Smith webpage, see page 18 at
http://www.hotwater.com/lit/training/320991-000.pdf
"the thermocouple is not a separate replaceable part."

Thank you for locating that training information as it sure does seem like
they designed the $10 thermocouple to not be replaced easily!

The existing thermocouple is attached at two points, one of which is
screwed on at the S-shaped 180 degree C thermoswitch (which seems easy to
remove) but the other of which is seemingly firmly attached to a plate that
also has the pilot light tube just as firmly attached.

So it seems that the thermocouple can't be 'wiggled' out, although I
haven't tried using real force yet.

> "There is no routine service associated with the TCO"

It's only slowly dawning on me that the thermal cutoff switch (TCO) is
making the thermocouple not "universal".

"The TCO is an integral part of the thermocouple and
not replaceable as a separate item. A pilot burner assembly must be
reinstalled."

See picture and instructions on page 20

That manual was *fantastic*.
Thank you for finding that!

I'm not sure how you knew I had an AO Smith hot water heater, but I do.

I called the residential service number listed in that manual at
800-527-1953 (x2 x2 x2 x1) and spoke to a very nice support person who
explained that there are two filters that need to be cleaned just as
described in that wonderful training manual.
1. Cordorite (she called it chromatic) anti-flame filter
2. LDO (she called it metal mesh) dust and anti-flame filter

Not knowing your specific model & serial numbers, 2 possible parts are
shown at
https://www.wallingfordsales.com/products.asp?cat=564&pg=68
P/N's 9006013005 or 9006014005

The lady at AO Smith asked for my serial number, and given that, she told
me what you said, which is that the thermocouple with Thermal Cutoff Switch
is not replaceable.

She said I need the $88 MSRP pilot assembly PN 9003455005 which she said I
should be able to get in San Jose at:
- Slinky Brothers 408-494-7948 (7-4:30 M-F)
- RV Cloud 408-378-7948 (they don't sell AO Smith anymore they said to try
a place named "rubenstein on monterey highway who is not open on weekends)
- TW Smith 408-249-9880 (they're not open on weekends)

 

[Danny D.]

On Sat, 20 Aug 2016 14:02:54 -0400, Retired wrote:

> You're welcome

That manual was great. Nice color pictures. Nice explanation.
And it had the all-important AO-Smith 800 number which is really good (and
far better than Sears and Honeywell, both of which were horrid).

FWIW, I did a Google Images "Search by Image" of one of your pics,
and got a good hit on an A O Smith web page. (google is your friend ;-) )

I'm amazed that your image search worked, but I appreciate you doing that
as the sticker on the side of the AO Smith water heater had a sears number
so I had called them first (and wished I had not) since they gave me the
wrong part number (which I could tell was wrong from looking up what it
looked like).

I called the AO Smith people back and got another nice person, who kindly
is sending me, gratis, an AO Smith Filter cleaning kit PN 9006477005.

Googling, here is a picture of what I think they're sending me:
https://www.johnstonesupply.com/storefront/product-view.ep?pID=N45-884

That google search also found this 2015 AO Smith parts catalog:
https://www.hotwater.com/lit/catalogs/apcom_aos_catalog_w_slip_sheet.pdf

This seems to show two part numbers for the propane pilot assembly:
9003455005 & 100109243

I wonder if I should add the sacrificial anode to my list of parts to get?

Mine is under the hot water nipple, where the part number includes the hot
water nipple where a minimum order is $50 at (800) 433-2545
AO Smith Sacrificial Anode 9009148005 $38 + $10 UPS Ground

Do you guys replace anodes at around 10 years?

 

[Danny D.]

On Sat, 20 Aug 2016 12:39:36 -0500, CRNG wrote:

Why do you think the resistance matters? Did you put a replacement one
without the thermal fuse in and does it work? If it does, end of story
on the resistance part.

+1

I'm not a plumber so I don't know if the resistance matters or not, but I
do know that the thermocouple generates 30mv which is puny so any
additional resistance to the 24 inches of wire could make a difference and
I don't know what the resistance of the 180C thermal cutoff (TCO) is.

If the 180C thermal cutoff adds appreciable resistance, then the resistance
of a 24-inch universal thermocouple will be different than the resistance
of this 24-inch thermocouple with TCO such that it won't be 30mv anymore.

But putting a replacement thermocouple seems to be far more difficult than
people make it out to be, simply because AO Smith designed this as a
non-replaceable part. It can only be replaced as a "pilot assembly", part
number 9003455005.

 

[Retired]

<snip>

That manual was *fantastic*. Thank you for finding that!

You're welcome

I'm not sure how you knew I had an AO Smith hot water heater, but I
do.

snip

FWIW, I did a Google Images "Search by Image" of one of your pics,
and got a good hit on an A O Smith web page. (google is your friend ;-) )

 

[Danny D.]

On Sat, 20 Aug 2016 16:59:13 -0400, TekkieŽ wrote:

> Thank government regulation.

Just to report back, the sandpapered thermocouple has been working, so I
have time to order the correct parts, probably from AO Smith themselves as
they have an order number for parts:

When I buy the pilot assembly, should I buy an anode?

I have hard water (calcium carbonate rich).
How often do you replace your anodes?

 

[Jerry Peters]

In sci.electronics.repair Danny D. <dannydiamico@yahoo.com> wrote:

On Sat, 20 Aug 2016 16:59:13 -0400, Tekkie? wrote:

Thank government regulation.

Just to report back, the sandpapered thermocouple has been working, so I
have time to order the correct parts, probably from AO Smith themselves as
they have an order number for parts:

When I buy the pilot assembly, should I buy an anode?

I have hard water (calcium carbonate rich).
How often do you replace your anodes?

*If* you can remove it; there's very little of the aluminum or
magnesium rod still left, and you can see the supporting wires.

You should be checking the anode every year or two, this also keeps it
from corroding in place, so you *can* check it.

 

Danny D. posted for all of us...

On Sat, 20 Aug 2016 16:59:13 -0400, TekkieŽ wrote:

Thank government regulation.

Just to report back, the sandpapered thermocouple has been working, so I
have time to order the correct parts, probably from AO Smith themselves as
they have an order number for parts:

When I buy the pilot assembly, should I buy an anode?

I have hard water (calcium carbonate rich).
How often do you replace your anodes?

I don't have that type heater. You may want to see if you can get the anode
out. Might be a problem. I think I would procure the anode locally as I
think shipping may be expensive.

--
Tekkie

 

[tom]

"Jerry Peters" <jerry@example.invalid> wrote in message
news:npfmo0$6nm$1@dont-email.me...

In sci.electronics.repair Danny D. <dannydiamico@yahoo.com> wrote:
On Sat, 20 Aug 2016 16:59:13 -0400, Tekkie? wrote:

Thank government regulation.

Just to report back, the sandpapered thermocouple has been working, so I
have time to order the correct parts, probably from AO Smith themselves
as
they have an order number for parts:

When I buy the pilot assembly, should I buy an anode?

I have hard water (calcium carbonate rich).
How often do you replace your anodes?

*If* you can remove it; there's very little of the aluminum or
magnesium rod still left, and you can see the supporting wires.

You should be checking the anode every year or two, this also keeps it
from corroding in place, so you *can* check it.

Also, IIRC, it uses a large socket (1-1/8"?) and a long 1/2 drive breaker
bar . They are usually very very tight. Just drain a little water out
(gallon or so) and still you may need an extra hand to hold on to the tank.
You will need some clearance above the tank to put the rod in.

 

[pfjw@aol.com]

On Monday, August 22, 2016 at 12:40:54 PM UTC-4, Danny D. wrote:

I have hard water (calcium carbonate rich).
How often do you replace your anodes?

I don't, and will never have the need.

The summer house has a 17 year old propane fired Bosch Aquastar tankless unit that has performed flawlessly.

The main house has a WM Ultra gas-fired indirect heater that handles all our needs with a 96% efficiency rating.

The typical tank-type unit is about 40% efficient and has about a 10-12 year lifespan. Either of our two present systems has an indefinite life-span and runs over 90% efficiency. The WM unit carries a 30-year unlimited warranty in residential use - we are eight years in. The Bosch warranty ran out 2 years ago. But, still making HW - and as much as we can use for as long as we can use it, or the propane runs out, whichever comes first. As to cost, the Bosch was $425 17 years ago, the WM unit (with circulator and controls) was just under $1,000. As it was part of a complete heating system replacement, the incremental cost was minimal. And we have never regretted the choice.

Peter Wieck
Melrose Park, PA

 

[Allodoxaphobia]

On Mon, 22 Aug 2016 16:40:51 -0000 (UTC), Danny D. wrote:

When I buy the pilot assembly, should I buy an anode?
How often do you replace your anodes?

Me? heh...
I replece my anode every time I replace the H/W heater.

Jonesy

 

[Danny D.]

On Mon, 22 Aug 2016 16:26:25 -0700 (PDT), trader_4 wrote:

You will need some clearance above the tank to put the rod in.

They sell new ones that are in sections for people who have that problem.

Thank you for bringing the vertical space up as a problem, as I might have
that problem since the hot water heater is in a relatively small closet,
and it's on a pedestal off the ground.

I never thought of that problem until you mentioned it.

 

[Danny D.]

On Mon, 22 Aug 2016 20:19:12 -0000 (UTC), Jerry Peters wrote:

*If* you can remove it; there's very little of the aluminum or
magnesium rod still left, and you can see the supporting wires.

You should be checking the anode every year or two, this also keeps it
from corroding in place, so you *can* check it.

This makes a lot of sense to remove the anode yearly so that you can remove
it before it corrodes in place.

Unfortunately for me, the AO Smith anode (PN 9009148005) comes with the
hot-water nipple, so, they have it inline (somehow) with the hot water
pipe.

Seems silly to me that I have to basically disconnect the water pipes just
to check the anode.

 

[Danny D.]

On Mon, 22 Aug 2016 16:07:20 -0400, TekkieŽ wrote:

I don't have that type heater. You may want to see if you can get the anode
out. Might be a problem. I think I would procure the anode locally as I
think shipping may be expensive.

You have a point on the shipping, as the anode is long I presume.
Mine has the hot-water nipple on the end also.

I checked three parts stores.
None had it in stock while most had the pilot assembly in stock.

So, people replace the AO Smith pilot assembly more so than they do the
anode (or they use a different anode part number).

- pilot assembly 9003455005 $88
- anode with nipple 9009148005 $38

 

[pfjw@aol.com]

On Tuesday, August 23, 2016 at 8:12:43 AM UTC-4, Danny D. wrote:

On Mon, 22 Aug 2016 16:07:20 -0400, TekkieĹ˝ wrote:

I don't have that type heater. You may want to see if you can get the anode
out. Might be a problem. I think I would procure the anode locally as I
think shipping may be expensive.

You have a point on the shipping, as the anode is long I presume.
Mine has the hot-water nipple on the end also.

I checked three parts stores.
None had it in stock while most had the pilot assembly in stock.

So, people replace the AO Smith pilot assembly more so than they do the
anode (or they use a different anode part number).

- pilot assembly 9003455005 $88
- anode with nipple 9009148005 $38

You do realize that you have, at best, a 50% chance of replacing the Anode without damaging the tank? And with this in mind, and if this is your intention proceed as follows:

a) Identify an immediate source for the Anode. DO NOT buy it, simply identify the source.
b) Only then remove the existing Anode. If you get it out without additional damage to the tank, and if the threads are clean, only then purchase and install the new Anode.

Imagine how you would feel if you purchase the new unit prior to removal of the old - and then found the tank to be unusable...

And, I really hope that your family has not been without hot water since the 19th? Today being the 23rd? That would just be nuts!

Peter Wieck
Melrose Park, PA