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How do I tell if a Thermostat is bad?

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winner155
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Posted: Sat Nov 10th, 2007 04:35 pm

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I have a behemoth 120 g Rheem electric water heater. Of late, only the first person who takes a shower gets hot water. I replaced both of the heating elements ( which looked quite clean) but I now note that when the water heater is on and I use my tester I can get the tester to light up when I touch it to the upper heating Thermostat and the two wire attached to the heating element but not when I touch anything on the lower element or thermostat. I spilled one heck of a lto of water when I replaced the elements(I did something so stupid I will not describe it here or anywhere for that matter) and I wnat to know if the lower thermostat is bad and if I replace it, will that solve the problem? Any suggestions on next steps to take or how to test the lower thermostat? Should I just go ahead and replace the lower thermostat?

eleent
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Posted: Sat Nov 10th, 2007 07:21 pm

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Hello: You're still alive, so clearly, you could have messed up more than you did

With cold water in the bottom of the tank, turning the adjustment on the lower thermostat up and down as far as it will go should produce a slight "snap" as the switch inside connects or disconnects. If you do this with power on and have your meter on the terminals of the lower element, you should see a change in the voltage. If there is no power going to the lower thermostat, the upper one may not be switching correctly, or the upper part of the tank may not be heated up enough to switch power to the lower thermostat. Heaters are usually wired so the upper elemet has priority.

You are dealing with 240 volts here and you may already have used up one or more of your lives. So, get help if you need it. You need a volt/ohm meter to do the tests needed to know what's going on.

Did you check the condition of the dip tube? You night be able to see it by looking into an element port. May luck be with you!

Yours, Larry

energyexpert
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Posted: Sat Nov 10th, 2007 07:31 pm

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Thermostats in an electric water heater only control one leg. Power is always available on one side and will feed through the element if the element is good. The top thermostat supplies power to the top element until the top of the heater reaches setpoint. Then power is interrupted to the top element and tranferred to the lower thermostat.

Check Tanklets and Electric Water Heater Issues for troubleshooting.

David

winner155
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Posted: Mon Nov 12th, 2007 04:00 pm

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Thanks for the reply. Had a friend who had the right meter come over and one of the elements was indeed bad. We checked the relay between the upper and lower elements and they are working and the thermostats are also working, One question we had was if the upper thermostat should be set lower than the lower thermostat, That made sense to us as the lower one is the one you would want to heat the entire tank and the upper one should kick in while water is actually being used to extend the time you have hot water, I have four kids and two of them think they need to wash the sins of the world off of them every time they shower and we have not had a problem before since we bought the house three years ago, My previous experinece has been for twenty years getting hot water off of the oil burner and using a water tank that runs as if it was one of the zones on the oil burner and I have little experience in hot water heaters. You would think that I was supplying hot water to the world with the $400 electric bills I get to run lights, fridge and hot water.

winner155
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Posted: Mon Nov 12th, 2007 04:03 pm

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energy expert

Thanks, please see my note I think I have it solved. Will find out Tuesday morning when everyone takes a shower and see if I get the call on my cell complaining about hot water. DO you know the temp settings that are normal for the upper and lower thermostats. I want to maintain hot water but also want to keep the electric bill below the GDP of a small nation..

winner155
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Posted: Mon Nov 12th, 2007 04:24 pm

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What is the best way to check the condition of the dip tube? Drain the tank and pull the lower element? Also, how do you know if the anode needs to be replaced. The water heater is approx 13 years old.

Tanks

eleent
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Posted: Mon Nov 12th, 2007 09:36 pm

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Hello: At thirteen years, the anode needs replacing. I wouldn't be surprised if your tank has two. Looking in an element port will show you where anodes are as well as show you the condition of the dip tube.

I usually set heater thermostats to the same 130* top and bottom. This is hot enough to slow bacterial growth and low enough to take a long moment to scald, allowing time to move out of the hot water. Manufacturers are tired of being sued for scalds, so they suggest 120*. This is only because folks haven't tried sueing manufacturers for Legionnaires infections ... that I know of

Yours, Larry

winner155
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Posted: Tue Nov 13th, 2007 09:08 pm

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Thanks very much. Didn't even think about microbes in the hot water, nice to make me afraid of taking a shower. One more thing to obsess about.

Peewee
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Posted: Mon Nov 26th, 2007 04:31 pm

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I have the same problem. I drained the tank to replace the bottom element, not knowing it didn't get power until the top one was done. This is a new house for my son and was trying to get hot water. Did replacing the bottom element work and how long did it take to heat the water?

Thanks,

peewee

Peewee
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Posted: Mon Nov 26th, 2007 04:31 pm

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energyexpert
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Posted: Mon Nov 26th, 2007 08:03 pm

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Peewee,

The thumb rule is that 4500 watts will heat 20 gallons per hour 90 F rise. For example: if inlet temperature is 50 F a 40 gallon tank will be heated to 140 F in about 1.5 hours since only the water above the lower element is heated; the bottom few gallons remain cold.

David

Peewee
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Posted: Mon Nov 26th, 2007 10:04 pm

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David,

Then there must be something else wrong as it never heated all day, about 5 hours. There is juice to all the terminals, we checked the breaker, made sure there was no air in the tank. The hot water side drains of the top and the cold tube goes all the way to the bottom, is that right? I have no other idea of why it won't heat. Any other suggestions?

Thanks, Peewee

energyexpert
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Posted: Mon Nov 26th, 2007 10:42 pm

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Peewee,

You said there was "juice at all terminals." Were you measuring terminal to terminal or terminal to ground? A WH thermostat only opens one leg so you will always have juice on all terminals if you measure terminal to ground.

Go to Tanklets and then to Electric WH Issues. You will see a picture there of an upper thermostat and upper element. The top thermostat supplies power to the yellow wire going to the top element until the top thermostat is satisfied. Then power is switched from the yellow wire to the black wire which goes to the lower thermostat. If you have 240 volts across the top element and the water does not get hot, your top element is open (bad).

If you find this to be true and want hot water soon without changing the top element, turn off the power and completely remove the yellow wire from the WH. Determinate the black wire going to the lower thermostat from its screw and reland on the thermostat screw which before had the yellow wire.

Turn on the power. The whole tank will now be heated from the lower element. But no quick recovery.

David

Peewee
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Posted: Tue Nov 27th, 2007 02:52 am

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David,

Thanks, I will try that to see. We were told the bottom one was bad when in reality, it might be the top one. Thanks again,

Peewee

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