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

On Tue, 23 Aug 2016 05:33:09 -0700 (PDT), trader_4 wrote:

I took apart another water heater today, and found interesting thigns.
The anode was white and mostly gone.
It took an 8-foot long pipe to get the 27mm plug out (but the water heater was spinning which made it harder).
Both the hot and cold water nipples have some kind of plastic restrictor in them (why?).
The flue had a spiral pipe going through it.
The safety valve has a spring inside and was gunked up. The output valve was all gunked up with white creamy stuff.
The thermostat screws off (using a hammer!) and it had a six inch or so long tube going into the water tank which was all gunked up.
Rust is everywhere.
But I was easily able to remove the thermocouple from this water heater (but not from the AO Smith water heater).
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Are you sure it's the hot water side? Usually if it's not a separate rod, it's part of the cold water inlet tube which introduces the cold water at the bottom of the tank.
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On Tue, 23 Aug 2016 20:12:50 -0000 (UTC), Jerry Peters wrote:

I'm not sure of anything but that's what the AO Smith technical support told me on the phone.
Taking the suggestion from others, I measured the headroom to only be about 10 inches above the water heater - so I don't really think I can get the old anode out without removing the entire water heater, which I don't really want to do.
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Doesn't seem like it, especially if it's part of the water inlet tube. For low clearance separate anode rod applications there's a special replacement rod that has periodic narrow sections, so you can bend it to get it to fit.
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On Mon, 22 Aug 2016 16:40:51 -0000 (UTC), Danny D. wrote:

Me? heh... I replece my anode every time I replace the H/W heater. :-)
Jonesy
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On Sat, 20 Aug 2016 08:24:06 -0400, Retired wrote:

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)
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<snip>

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

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: 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?
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On Saturday, August 20, 2016 at 12:14:02 AM UTC-4, Danny D. wrote:

No, because this is the first time I've seen or heard of this thermal fuse. But my last WH is 15 years old and IDK what's in new ones.
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On Sat, 20 Aug 2016 06:00:10 -0700 (PDT), trader_4 wrote:

Thanks to Retired, the moment I talked to the nice lady at the AO Smith phone number in his training manual, I realized that the thermal fuse is a 180C thermal cut off which self resets after a few minutes.
But I don't think the TCO is my problem. I think my problem is the thermocouple but sandpapering the 2-inch thermocouple last night seems to have helped keep the pilot going so I am ok until Monday when I can call local suppliers for the $88 AO Smith pilot assembly part number 9003455005.
However, what I didn't know was that the nice AO Smith lady told me that I should be cleaning two filters on the water heater every six months, which are the flame arrester (non replacable) or filter screen (replacable) which she said is explained in a video here: http://www.hotwater101.com/video/gas-gascontrol-filtercleaning.html
She also referred me to a filter-cleaning PDF here: http://www.hotwater101.com/pdf/st-gas-filtercleaning.pdf
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On Friday, August 19, 2016 at 9:21:44 PM UTC-4, Danny D. 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.
The real issue I see is if this is just additional protection or is it protection in place of other protection that a typical WH would have? I would guess it's probably additional, but IDK and it's your WH.
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On Sat, 20 Aug 2016 05:58:32 -0700 (PDT), trader_4

+1
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On Sat, 20 Aug 2016 12:39:36 -0500, CRNG wrote:

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.
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On Sat, 20 Aug 2016 05:58:32 -0700 (PDT), trader_4 wrote:

I think resistance matters because we're talking millivolts here, but most people, from what I've read, seem to match resistance simply by matching length - so for me - that part is easy since it's a 24-inch long thermocouple.

I'm ok without the "additional protection" which, as I understand it, only comes into play when the bottom of the water heater is at a certain temperature high enough to blow the thermal fuse.
Since I can read a "180" on that thermal switch, for now I'll assume it triggers at 180 degrees although I don't know if that is C or F.
http://i.cubeupload.com/Qh4PMI.jpg
Given 180C = 356F and that 180F = 82C, I guess it could be either way as neither temperature should happen in a house - but it's probably C.
Rest assured, I would love to put in the $10 24-inch 30mv Honeywell CQ100A1013 "universal" replacement thermocouple - but it just will never fit unless I entirely rebuild the bracket assembly.
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