Hot water not hot enough!


Is it possible that the new water heater thermostat I bought was no good? Or does this sound like something else?
Sorry for the complicated story:
This is a two element, two thermostat Sears 51 or 52 gallon water heater**. **I appreciate that someone explained the details of
When I first installed it, the water heated to 180 degrees and I had to turn off the power. After I used the hot water, I turned the heater on again and again it went to about 180 and I turned it off again.
The third time, it didn't get too hot, in fact it didn't get hot enough, only about 110. But I used it at 110 degrees for a couple days, and then turned up the thermostat from "hot" to "hotter". That made it about 125 iirc, and finally I turned it all the way up, and now if I take a bath it is just a bit hotter than my feet can take, maybe 130 or 140 and I have to add about 10% cold water. It used to be I had to add about 50% cold water to get the right temperature. So now I run out of hot water very quickly, and can't take a re hot bath, only a warm one.
Was it a bad thermostat from the start? Did heating the water to 180 damage the heating element, maybe cause a short half way along, so that only a half of the heating element is running? Wouldn't it still get as hot as it used to if I waited long enough? (I've waited more than a day without using hot water, to see if it would get hot.)
If the water gets cold enough, the top element goes on, and the red light there goes on. After 20 minutes, the light and the top element go off and the bottom element goes on**.
The reason I bought a new thermostat in the first place is that the water got so hot it tripped the bottom heat limit switch. I reset that once and it did it again, so that meant the thermostat was bad.
Could heating the water four times to 180 degrees have damaged the lower element, or is it more likely the thermostat was letting it get too hot the first couple times, and not hot enough now?
I could test the thermostat in a pot of hot water on the stove, but I think I will end up getting it wet on all sides if I do that. Will that damage it?
**I appreciate that last time I asked about this, someone explained the details of how two element heaters work.
Thanks
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mm wrote:

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I would explain how the wiring works, but the site Buffalo gave you is excellent. If you change thermostat(s), make sure you have good contact between the thermostat and the tank, as this is how it senses the tank temperature, so if it loose, it won't read correctly and it will overheat

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RBM wrote:

Yes, I always put a dab of thermally conductive paste (from an electronics supplier) on the bottom of a thermostat when I have occasion to change one. Not essential, but just to "make sure".
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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