Hot Water Heater went Nuts!

[slim]

Reliance Water Heater
Model 5 40 20RS 960
Ser. K981 770 71

This unit has been acting up in the last yr. and now has me scared to death about blowing up!
Seems about a yr ago, even on the low setting sometimes the water gets so hot the water smokes coming out of the pipes, i have turned down the temp. control to its lowest setting and then the unit worked fine for 6 months, but now is acting up again!
It got so hot it was scary so i turned off the breaker and drained all hot water, but then when i turned braker on it was steaming agin and then for the first tme ever kicked off the re-set button!
But i am concerned the unit may blow up?
So the temp control seems to hang or is now hung on super hot?
Should i first replace the the upper high temp thermostat or the lower or both? Dont have any equipment to check!
Thank you, very much!

[JWWebster]

did you completely refill the water and get all the air out? If not you is gonna need some new elements

[slim]

Sorry, i should have been more specific, i did not drain the hot water out of tank, but let it run till it got cold in the Bathtub, since then i turned the setting to the lowest and it stii is getting burning hot!
When i find out which Thermostat i should replace, i will pull it and get another one, on the high-temp one on top there are no adj. to be made. Those can only be made at the bottem, low temp one!
Thank's for any help!

[JWWebster]

The way it works is, the bottom thermostat does most of the work, both elements do not come on at the same time. If they did then a breaker would be thrown,(too much load). The bottom heats and clicks out then the top one kicks in and finishes the heating. You should replace both top and bottom thermostats and be done with it.

[jumptrout51]

They are cheap. Replace them both.
Most importantly, make sure the T-stats are touching the tank at the rear of the t-stats. Make sure there is no rust buildup between them and the tank.