Marathon element leaking

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Answer: -The Marathon backplate is not shown on the Rheem parts sheet. Parts sheet .pdf
-Rheem might sell the replacement part.
-The corresponding part on regular heater is called a thermostat clip, but it is NOT the same and won't work on the Marathon.

Answer: -Yes. The Marathon backplate is necessary to conduct heat to thermostat.
-If the plate is not in contact with the opening for the element, then the thermostat will misread temperature and cause overheating. The result is tripped reset button on upper thermostat at 170-180°F ... but if upper thermostat is not functioning, then water will be released from TP valve at 210°F to prevent steam explosion.

-Is the damaged metal plate caused by
a) water leak or
b) some type of current corrosion caused when different metals are in contact with each other, like the metal element and metal plate.

Note from this website:
Check specs on tankless. Some models will not activate if incoming temperature is too high. However you can fill the marathon with hot water, as planned, then install mixing valve. The mixing valve will add cold to the hot water as it leaves tank ... letting you adjust the hot down a bit so water going to tankless does not exceed the sensors on tankless.

If the deteriorated plate was caused by leak, one can argue that leaking elements are not rare, so the backplate is not suitable or merchaniable for the product.
Certainly Rheem is aware of this problem, and a case can made for warranty coverage on the whole tank, as long as this is residential installation depending on age and model and warranty at time of purchase..... or at least get a replacement part.

Question from Robert: I have a Rheem Marathon 50 gallon short water heater. Sorry to bug you with what will probably be a silly question, but what is the name or part number for the metal plate that the thermostats are mounted to? They kind of wrap around the element (which seems to be what holds them in place) and rise above it. It looks to be galvanized steel? In any case, my lower plate has completely corroded through, which then caused the lower element run continuously and boil water out of the T&P valve. The upper plate is not far behind. Any idea where the heck I can find a couple of these?
Lee emailed with same problem Question from Lee: Question: Is the “thermostat bracket” replaceable? I have looked all over for a replacement. Answer: -The Marathon backplate is not shown on the Rheem parts sheet. Parts sheet .pdf -Rheem might sell the replacement part. -The corresponding part on regular heater is called a thermostat clip, but it is NOT the same and won't work on the Marathon. Question: Is the corroded portion necessary to transfer heat to the thermostat? Answer: -Yes. The Marathon backplate is necessary to conduct heat to thermostat. -If the plate is not in contact with the opening for the element, then the thermostat will misread temperature and cause overheating. The result is tripped reset button on upper thermostat at 170-180°F ... but if upper thermostat is not functioning, then water will be released from TP valve at 210°F to prevent steam explosion.
Larger image Larger image Image on right shows Marathon element and thermostat that is not damaged. What to do about damaged metal plate: -Call Rheem and explain the problem, and tell them others have experienced same problem. This means Rheem should sell a replacement backplate. -A metal shop might able to cut a duplicate backplate out of aluminum. Or cut your own using some metal material. -Search internet for '1/16" aluminum plate' For example, Buy 12x12x 1/16" at Amazon -A roofing company might have metal stock -A glass company might have something. -Galvanized would probably work, but would rust. -Aluminum flashing would be too thin, but maybe layer aluminum flashing under the damaged plate and attach both pieces? Warranty coverage: 2020 warranty sheet Earlier warranty sheet Another warrant sheet The Marathon warranty excludes damage cause by leakage, so the question becomes: -Is the damaged metal plate caused by a) water leak or b) some type of current corrosion caused when different metals are in contact with each other, like the metal element and metal plate. Consiter the type of metal: If the plate is made of aluminum then water leak will not damage aluminum. For example aluminum patio covers, aluminum storm doors and aluminum windows are not damaged by rain. Leaking and water quality: - A rusted or deteriorated backplate might cause a leak. or moisture of some sort. If the water is particularly acid, or has some other treatment issue, it can become reactive with metals.. especially steel, and might react with aluminum.
Follow up email from Robert: Thanks, but the metal plate is actually not rusted. It has a bunch of white goo that is eating through it by what I can only assume is some sort of electrolysis (I'm an auto mechanic so this is the best way for me to describe it). The seals at the elements started seeping about six months ago and I've been so busy with trying to renovate the house that I put the heater on the back burner. This morning the water was boiling out and I discovered thermostat was no longer attached to the tank wall. Trying to find that part, especially on a Sunday, was making me crazy. Answer probably needs immediate attention before it costs you a water heater.... the element leak could rust out the threads in water heater ... unless the threads are brass ... once threads are damaged, water heater is done. 1) Remove elements, use 1-7/8" socket... and see if you can seal using teflon tape or T2 teflon pipe sealant ... until new elements arrive, or you find suitable high-heat washer. 2) While lower element is out, use shop vac with various size plastic hoses taped to vacuum hose to clean out bottom of tank. Resource: Water heater will not drain Follow up 2 from Robert I had assumed the element ports were brass. Didn't occur to me that they could be steel! I'm going to drain that sucker tomorrow. I'll let you know how it goes. Follow up 3 from Robert The element threads look pretty brass like to me, and don't seem damaged. I have both the elements out and they look like the elements are made from different materials. The long one came out of the bottom. I also shoved my work light in the top port and looked into the bottom. It was amazingly clean. I mean, AMAZINGLY. The dip tube looks pretty good, too. I have new gaskets on the elements and I'll tape up the threads. Hopefully that'll keep them from leaking. I'm not sure what I'm going to do about the bottom thermostat yet. Answer: It appears the element ports are brass. Lucky there. You need new washers on the elements for sure.. Couple things to check: 1) Household water pressure should be around 50 psi ... Over 80 psi can cause problems ... and might cause water leak at heater. Use a pressure gauge on the drain valve. . water pressure can spike sometimes if you're on city water... Here's a pressure gauge tester: Resource: Pressure tester 2) The rubber washer is supposed to seal on the metal rim at the element port ... Clean the rim real well and inspect for a smooth surface ... if surface is pitted, then rubber seal will not function ... 3) Closed system can cause too much pressure .... which is caused by a check valve or pressure reducing valve and sometimes a recirculation system .... install expansion tank anywhere on cold water line near water heater... this will reduce pressure that might cause leak. Resource: Expansion tank 4) Unlikely, but the Vacuum relief valve on Marathon might cause problems .... ''The vacuum relief valve provides a means to eliminate the negative pressure or vacuum by admitting air into the tank to equalize the pressure.'' I'm not sure that a vacuum would contribute to the problem you're experiencing ... but possible that your vacuum relief is bad? and you're getting a vacuum that deforms the tank slightly and then corrects itself ... creating possible leak conditions that have continued over time...?? Resource: Vacuum valve
Solution by Lee: I believe I have the tank fixed now so I am not planning to contact Rheem at this time. The electrolytic corrosion theory may be a factor, but I know there was a small leak as well. When I first pulled everything apart the lower cover insulation was slightly wet. I was able to fab a new plate from 1/16 aluminum. I used a 1-½" electrical knockout as template, which produces a 1-7/8” clean hole. Maybe a hole saw would work, but I kind of doubt it. Then I took it the rest of the way with emory paper and a dremel tool. The hole size needs to be somewhere between 1 7/8 & 2”. (This was trial and error until I got it to fit) It needs to be tight enough to “press on”. It would have been easier to get it on if I had some really shallow throat C-clamps, but I didn’t. I had to push it on by hand. I didn’t want to “hammer” it on because I was afraid of causing a leak between the brass fitting and the tank. I’m going to order some spare gaskets for the elements. I’m 99% sure these are the correct ones. (Part # SP310060) I installed new elements and gaskets. (Part # SP210201) This was the whole reason I found the issue. I wanted to install lower wattage elements so I could use the water heater to dump excess solar energy. (I installed 3000W elements instead of the factory 4500 watt units.) The Marathon will now preheat water going to our on-demand gas water heater. (We just switched our water heating to gas last winter) Note from this website: Check specs on tankless. Some models will not activate if incoming temperature is too high. However you can fill the marathon with hot water, as planned, then install mixing valve. The mixing valve will add cold to the hot water as it leaves tank ... letting you adjust the hot down a bit so water going to tankless does not exceed the sensors on tankless.
Thermostats The mechanical thermostats on water heaters are bi-metal switches ... like the old HVAC thermostats before they changed to digital thermostats ... so water heater thermostats are approximate at best. This means you cannot get exact temperatures, and instead can adjust thermostat to reach a comfortable set point. Calibration for residential thermostats Minimum temperature 90° Maximum 150° Thermostat differential 17-27°F ... temperature can drop significantly before heater turns on. IF thermostat is not functioning correctly, then suggest you buy another one and avoid effort for warranty coverage. All values +/- 5 Resource: Identify thermostat Wrong temperature If your element is not touching the aluminum plate, then it might not have sufficient contact for the thermostat to register correct temperature ... and you might have to add step flashing to build up the thickness Warranty coverage Another thing ... warranty on metal backplate ... Pput the old backplate in water and see if it deteriorates further, and that tells if the problem was caused by electrolysis ... or leak ... or maybe the deteriorated part caused the leak. If the deteriorated plate was caused by leak, one can argue that leaking elements are not rare, so the backplate is not suitable or merchaniable for the product. Certainly Rheem is aware of this problem, and a case can made for warranty coverage on the whole tank, as long as this is residential installation depending on age and model and warranty at time of purchase..... or at least get a replacement part.