Electric water heater only stores 10 min of hot water

6 years ago

Hey all. I have a 50 gallon Rheem electric water, installed in 2010, that I'm having trouble diagnosing. I only get about 10 minutes of shower time before the hot water is about gone, so we have to wait a while between family members showers. I checked our shower's gallons per minute and it was about 2. Both thermostats are set to 120 degrees. It sure seems like the lower heating element isn't working, but I already checked the heating elements, the top was 12.7 ohms and bottom was 11.6 ohms. I also did the continuity test on the thermostats and they seemed to click on and off properly, and my multimeter verified the circuit opened/closed accordingly. Is there anything else I can try, to diagnose it? Any advice is greatly appreciated, thanks!

-Marc

Featured Answer

klem1

6 years ago

"There is nothing magical, mystical, or complicated about a residential water heater."

But as witnessed by sounds they make,water heaters sometimes have a disposition.

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Comments (9)

DavidR
6 years ago
From what you write, you may know this already, but an electric WH is wired so that the top thermostat is the one that takes the lead, heating the top half of the tank for a quick recovery. Any time the top water is below its setpoint, the top element is on and the bottom one is not.

The top thermostat is actually a double-throw switch. Once the top thermostat is satisfied, you have half a tank of hot water. The top thermo reroutes the incoming power from the top element to the bottom thermostat. The bottom thermostat then hammers the bottom element until it's satisfied, then it shuts off. Now you have a full tank of hot water.

This allows you to have 2 high power (4500 Watt or whatever) elements but a WH that never uses more than 4500 Watts.

It sounds like your tests seemed to show the elements and thermostats working right. Now you need to actually monitor what the upper and lower elements are doing while the tank is in operation.

This requires working with hazardous voltages, so while I don't want to offend you by suggesting anything, I have to say right here that if you don't know electricity and electrical safety by heart, you should turn this over to a qualified service technician.

That warning out of the way, this is pretty easy to test with the access panels off,; insulation peeled back; and neon test light, DMM, or Wiggy at the ready. For something like this I'd probably connect a test light to each element with insulated clip leads, so I could watch the transition from top to bottom element happen (or not happen).

My guess: you'll find that the top thermostat's contact that closes on temp rise, the one which transfers power to the bottom element, is not closing properly or consistently.,

Another possibility is that although the bottom element measures the right resistance for 4500-5000 Watt WH, and the top thermo is working right, the wiring between top and bottom elements has failed. Probably close to 50 years ago, I rewired a WH on which that had happened. Maybe the wire that failed had been nicked when it was pulled in at the factory or something, but for whatever reason, it had burned in two about 1/3 of the way from top port to bottom port.

Let us know how you make out with this.
Marc
Original Author
6 years ago
Ah thanks for the advice! Yeah I am a bit afraid to do a live voltage test, but it looks like for $30 I can get a full replacement kit on amazon that comes with new thermostats and elements, so I'm just going to replace everything and hope it fixes it =)
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Kaffine is correct. A circuit breaker will trip if there is excess current draw - meaning an overloaded circuit or a short circuit. It doesn't trip if a high resistance connection heats up unless that causes the surrounding insulation to break down and results in a short circuit. What you saw isn't all that uncommon on heating type appliances or anytime a circuit is cycled at near its max working ampacity. If there is a loose connection, the connection heats up and the wire expands a little. Because the wire is expanding, it also deforms slightly - as does the terminal. When the power shuts off, the connection cools and is now a little bit looser than before because all of the mating parts have deformed slightly. In addition, the heat causes the wire and terminal to oxidize. The oxide isn't a good conductor of electricity and also increases the resistance of the connection. This cycle is repeated every time the heating element turns on and off. As the resistance of the connection increases, it becomes the "heating element" performing basically the same function as the element that's in the tank. To prevent this type of failure, it's important to make sure that electrical connections have good surface area contact and that terminals are tight. On larger connections and aluminum cables, anti-oxidant compounds are used on the wire to prevent the oxidation cycle. In larger installations, preventative maintenance involves scanning a bus, breaker panel, etc. with an infrared thermometer to check for "hot spots" that would indicate a deteriorating connection. This is also why all electrical splices must be in a box. My guess is that there was nothing that would burn near that connection - and that's by design. BTW: There are new breakers out that detect arcing - not just excessive current flow. They are more expensive, but will interrupt this type of problem if it gets bad enough to arc. Any parts that have shown excessive heating should be replaced. In addition, trim the wire if you have some additional length so that the connection is made with wire that isn't damaged with oxidation.
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klem1
6 years ago
"I'm just going to replace everything and hope it fixes it"

May as well replace the dip tube also because it causes same problem described.
M
6 years ago
And then install a new sacrificial anode. In fact, you should have checked it regularly and replaced it as needed. That's one of the best ways to extend the lifetime of any water heater
DavidR
6 years ago
If the problem is the second scenario I described above, replacing the thermostats and elements will be a waste of money.

Before you do that, I suggest that you turn off the breaker (lock it out, if possible, or make sure no one touches it) and verify continuity of the wiring from top access port to bottom port.

If you have to replace any wiring, use wire rated for at least 90 deg C. Might as well replace it all.

Also test the top thermostat's normally open contact (closes on temperature rise). First, allow the heater to heat the top water until it shuts off. Turn off the breaker. Now set the upper thermostat to its lowest temperature. With a DMM or VOM set on resistance, check for continuity between the thermostat's LINE terminal and the terminal that goes to the lower element. It should read zero ohms. If not, replace that thermostat.

Good luck! Let us know how it goes.
User
6 years ago
Your fill tube has failed. The tank is 10 years old. Average life is about 6. You are ahead of the game. Get a new water heater.
STEVEN PENALUNA
6 years ago
Have had this same problem in the past and had to replace water heater because of white scale that looks kind of like gravel filling the bottom half of the tank.
User
6 years ago
There is nothing magical, mystical, or complicated about a residential water heater.

Electric water heater only stores 10 min of hot water

klem1

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DavidR

Marc
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Electric water heater only stores 10 min of hot water

Comments (9)

MarcOriginal Author

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Marc
Original Author