Resistance of thermal switch in thermocouple - does it matter - hot water heater - generic replacement

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?

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I bought a generic Honeywell 30mv 24-inch thermocuple (PN CQ100A1013) from Ace Hardware:

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That picture in the URL above is wrong because it's 24 inches:

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When I went to put it in the hot water heater, I belatedly realized the original thermocouple has an integral thermal switch.

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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:

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The thermal switch is a safety feature that will shut down the pilot if the heat under the hot water heater gets too great:

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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.

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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?

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Reply to
Danny D.
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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.

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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.

Reply to
Danny D.

I concluded the "universal" mount stood zero chance of fitting.

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There is just no way a "universal" thermocouple is going to stay put there.

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Just look at this bracket for my original thermocouple.

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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?

Reply to
Danny D.

According to this A O Smith webpage, see page 18 at

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"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

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P/N's 9006013005 or 9006014005

Reply to
Retired

Nomenclature is your problem here.

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

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

THEY ARE NOT INTERCHANGEABLE. Full Stop.

c) A THERMAL FUSE such as the one you picture is also a bimetallic device t hat opens at a specific temperature. Some such devices will reset, some wil l 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 t ime.

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 replacem ent is $143.00, think hard before buying a part over a new unit.

Peter Wieck Melrose Park, PA

Reply to
pfjw

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

Reply to
pfjw

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.

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

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

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)

Reply to
Danny D.

You're welcome

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 ;-) )

Reply to
Retired

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).

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:

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That google search also found this 2015 AO Smith parts catalog:

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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?

Reply to
Danny D.

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.

Reply to
Danny D.

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?

Reply to
Danny D.

Danny D. posted for all of us...

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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
Reply to
Tekkie®

*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.

Reply to
Jerry Peters

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.

Reply to
tom

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

Jonesy

Reply to
Allodoxaphobia

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

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

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

The typical tank-type unit is about 40% efficient and has about a 10-12 yea r lifespan. Either of our two present systems has an indefinite life-span a nd runs over 90% efficiency. The WM unit carries a 30-year unlimited warran ty 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 replac ement, the incremental cost was minimal. And we have never regretted the ch oice.

Peter Wieck Melrose Park, PA

Reply to
pfjw

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.

Reply to
Danny D.

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.

Reply to
Danny D.

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

Reply to
Danny D.

node

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 inten tion proceed as follows:

a) Identify an immediate source for the Anode. DO NOT buy it, simply identi fy the source. b) Only then remove the existing Anode. If you get it out without additiona l 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 th e 19th? Today being the 23rd? That would just be nuts!

Peter Wieck Melrose Park, PA

Reply to
pfjw

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