Water Heaters - Water Overheats & trips thermostat

I have a Rheem 40 gallon electric water heater. About a week ago, we noticed that the water was exceptionally hot. A day later, the thermostat kicked off. I reset it, only to have the problem reoccur. The second time, the breaker was tripped, as well. I replaced both thermostats, only to have the water get too hot yet again. I then drained and flushed the tank and replaced both elements. Same problem - scalding hot water. (The thermostats are set at factory 120, by the way.) I took the upper thermostat back and told them it must be faulty and exchanged it for another. AGAIN, tremendously hot water. A friend thought a wire may be grounded, but neither red nor black was at fault. We are completely stumped. Both the original and replacement thermostats are ThermoDiscs. They look identical but perhaps the wiring should be different? I am certain we wired them exactly the same, because we drew a diagram in advance - and futhermore certain colors only reach certain areas. I just don't know what to do next?? Obviously, I am not a plumber or an electrician, but I thought a water heater only had so many functioning parts! The breaker is shut off now, but I know that if I go back down and supply power, I will discover water coming out of my faucet at 200 degrees. Any suggestions would be sincerely appreciated.

Thanks, john

I received a response on the electrical forum which requires me to add more info. It was suggested that the back of the thermostat is not flush with the tank. Both the original and the brand new replacement are perfectly flush with no movement. We made certain of this when replacing it because of past experience. If you take the thermostat back off, the back of it is almost too hot to touch! I just cannot figure out why the heater is overheating so severely. New thermostats correctly fastened, new elements, wiring as before - no fix. WHY??

If you turn the tstat up high then back down do they click?
When you turn the heater on . Does just the top element come on and run till its hot there .Then does the bottom element turn on????

Good questions. I haven't tried toying with the thermostat to check for a click. Will do so. Likewise with the elements. After we replaced everything and filled her back up, I assumed it was fixed. An hour later, I checked the water at the kitchen faucet to verify everything heated up fine and was practically scalded! It was then the mystery began. I replaced the brand new upper thermostat with another brand new one and same thing. At that point, the tank and its contents were extremely hot, so I assumed when I turned the breaker back on the heater wouldn't start, but sure enough, you could hear the buzz when I placed my ear by the tank. What should I check for tomorrow morning? Right now, the breaker is off for the night. I hope to resolve this issue tomorrow. I really appreciate any help I can find here.

john

Im also back to how you have it wired????? When you first turn it on only the top is on later it goes off and the bottom one turns on.

With Ed here. If your stats and elements are good, that only leaves the wiring. I suspect the upper stat is miswired. Look at the instructions that came with the NEW stats and compare. Also, if you have a meter, you can save a lot of time. We need to determine which element is not turning off. This is easily done by measuring the voltage at each element before the safety trips.

I've had the wiring checked by an electrician, and he claims it is wired correctly. In fact, he insisted it HAD to work. Well, thirty minutes after he left, the thermostat popped! This MUST mean one of two things: it is wired incorrectly but in such a way that the electrician was fooled (I'm going to try another electrician) OR both brand new thermostats were faulty. Maybe a bad batch or something? I'll be sure to let you know what the second electrician tells me.

john

You may have a heater that is shorted to ground internally. The thermostat only switches one leg of the 240 volts. The other leg of the 240 volts is wired directly to the heater. If the wire inside of the heater is shorted to ground, internally, you will get 120 volts to the heater even if the thermostat is turned off.

Nashcat

This sounds logical, but how do I fix the problem? I'm at my wit's end.

Thanks!

john

Shut off the breaker, remove the wires from the elements, and check for continuity from each terminal to ground (the tank itself is ideal). The bottom element is more prone to this problem due to mineral build-up, so try that one first. The elements are switched only on one side, and if the element broke, the unswitched side will have 120V going through that side of the element to ground (the water heater) causing it to heat up. If this is the case, you can put wire nut on the wires going to the faulty element till you can get a replacement element. You will just have half the hot water you are used to till then.

I have a 50Gal Rheem that has done the exact same thing. EXTREMELY HOT water, then contantly tripping upper thermostat. I have drained (a bit of sediment) and reset the breaker several times in the past two days but it continues to happen.

Just curious.

Nathanial4

Get a complete rebuild kit and replace both elements and both thermostats and eliminate the constant trouble. Other than that there is nothing in there. The kits are cheaper than the sum of the individual parts anyway.

Ken

Agree with KField. I would like to add.....
In order to properly diagnose a water heater complaint, you really must have at a minimum, a digital volt meter. A cheap $10 unit will do just fine. The original post in this thread cannot be diagnosed because we don't even know which element is not shutting off.

Also, take a little time and study the wiring diagrams on the new stats. Try to understand its operation. This will go a long way in solving problems.

Hi,

I have the same problem with the water 40 gallon water heater. However I've had the upper thermostat changed 4 times with no luck. The plumber is completely dumb-founded. I am going to have a electrician come out but I have a feeling that won't help. I was told by "knowledgeable friends" that it might be the ground. I have had both upper and lower elements changed too. The plumber looked at the voltage going to each and it'd hooked up properly. Does anyone know why the thermostat is overheating??? And YES after the thermostat (that was removed) cooled down it clicked after turning the temp up. Everyone is completely stumped!!

PLEASE ANY SUGGESTIONS????

Desperate............

You didn't say if you changed the lower stat. If replacing BOTH stats doesn't help, I would then check for a grounded element. But this doesn't happen too often. You will need a meter for this.

There really isn't much to an electric water heater (I'm not talking about the units with a circuit board, I won't even go there). You have two stats, two elements and the wires.

No we didn't replace the bottom stat. Only the top one 4 times. I ended up calling Rheem (model I have) and they said I would need a meterand to call them back and they'd help walk me through. They suspected a bad ground and/or the element touching something it ought not to.

I am so frustrated. I think we may just go buy a new water heater and be done with this. I hope we won't have the same problems.

Replace the bottom stat, it's less than $10. In fact, the bottom stat tends to fail more often than the upper because it cycles more often. Stats are a common failure item for electric water heaters.
I'm a little confused as to why you replaced the upper stat 4 times.

Because that's where the reset button is. The "expert plumber" did it!! I thought that myself about the bottom one BUT I figured the plumber knows what he's doing. LOL

OK. The reset button is the symptom, not the problem. It's doing its job and protecting you. Perhaps you need a different plumber. It's actually pretty easy to change it yourself. The lower stat has just two connections. Be sure to turn off the breaker.

i'll try that tomorrow ty. I'll report back.

Well I'd like to report it appears that the bottom stat was fried! Something insode was melted onto the stat. All I know is that it was fixed! I was going to go do it myself BUT when I called the parts store they asked about the gauge of the wire that it could have something to do with it tripping. So it detoured me from buying it cause he said only an electrician would know. I hope this will be helpoful for the next person.

By the way I don't know if I am repeating myself or someone but the bottom stat tends to go more often due to sediment. That's what my plumber said.

HOT BATH TONIGHT!! YES!!!

Thanks for letting us know how it turned out. We wish more people would do the same so others can learn.

I think you meant to say that the bottom ELEMENT goes bad more often because of sediment in the tank. That is questionable. The lower thermostat does fail more often than the upper one because it cycles more often as was stated prevoiusly. The lower stat only gets power when the upper one is satisfied. Due to convection, the water heated at the bottom will rise to the top and make the job of the upper thermostat much easier. If the lower thermostat is stuck closed, it will heat the element every time the upper stat is not calling for heat. Since the lower is already producing more heat than is needed, the upper stat will never need to come on. As a matter of fact the temperature at the top will rise above 180 degrees which is the temperature that the manual reset button pops at and disconnects power to both elements. The fact that the reset button is on the top is irrelevant to the location of the real problem. An electrician would be better at troubleshooting the electrical part but if you needed an element, he may have been reluctant to tackle the wet part.

Glad you got it fixed. Next time try everything once before you try the same thing twice.

Ken