I am in the southeast US and have an electric hot water heater that is 25 years old (as is the house). Two years ago, I diagnosed and successfully replaced the lower thermostat. Earlier this year, because the high temperature limit switch kept popping, I investigated and replaced the upper thermostat (a Robertshaw model 5600 if it matters). Now, only about six months later, the high temperature limit switch opened again. I reset it and now have hot water again, but I want to get more than six months of maintenance-free service.
What I've tried so far
As mentioned above, within the last two years I have replaced both upper and lower thermostat units.
I have faithfully flushed the tank every year (we have some sediment from our well water). Neither the heating elements themselves nor the sacrificial anode have ever been replaced. I can detect no evidence of corrosion.
What I've done so far is to check the elements with a ohm meter. Neither element is grounded and each measures around 10 ohms. I have also double-checked the wiring and have found no loose terminals or bad wiring. I have also, after doing my checks on the system, turned the power back on and patiently listened as first the upper thermostat and then the lower one clicked off.
- What further diagnostic tests should I try?
- Should I just replace one or both heating elements?
- Should I just replace both elements and both thermostats "just because"?
- Should I just replace the whole hot water heater? (my wife wants this)
- Should I just learn to enjoy cold showers? (presumably after divorce!)
I'm not averse to spending time and money to fix this correctly, but I'd like to arrive at a more definitive diagnosis first.
Today, sixteen days after I originally asked the question, I noticed that the water was very, very hot coming from the tap. I went to the hot water heater with tools and noticed that the upper thermostat was definitely on and was definitely too hot, although the high temperature limit switch had not opened yet. I turned off the breaker, and checked and the thermostat was now open, and then turned the breaker back on. Is this sufficient evidence to declare the upper thermostat bad and in need of replacement?