Lukewarm water from drain valve


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Old 12-28-18, 07:15 AM
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Lukewarm water from drain valve

Went to drain or flush a few gallons from my electric water heater and got only lukewarm water for the three minutes it ran. Good news is no sediment I could see. But why only lukewarm water? Hot water had not been used for four hours. Shouldn’t it have been hot? New house to us, but nearly 20 years old. Been noticing that hot water did not seem to be lasting as long as we expected and wondered if that was because of the tank age or only a 30 gallon? Came from an indirect 40 gallon on a hot water boiler system.

Now I wonder if the lower electric element is out? Does that make sense as to why there is hot water but not a lot of it? We are a two person household.
 
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Old 12-28-18, 07:27 AM
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That is totally normal. Hot water rises and cold water sinks. So, the water at the bottom is always cooler. And, when you drain water from the heater new, cold water coming in enters the tank at the bottom making it even cooler.

If there is a problem with the water heater you'd likely notice it getting cooler toward the end of your shower or when filling the bathtub.
 
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Old 12-28-18, 07:30 AM
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Your observations suggest a problem in the lower part of the water heater. Wait three hours with no one using hot water. Open the lower hatch and measure voltage across the two terminals of the lower element. If you read 240 volts and that part of the tank is not good and hot (turn off breaker, measure voltage and see it is now zero) and then feel using your fingers then the element is bad.

If voltage across the lower element terminals never got to 240 then other components such as a thermostat could be bad. There are two thermostats, one under the top hatch and one under the bottom hatch.
 
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Old 12-28-18, 08:13 AM
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I understand cold water at the bottom and mixing cold with the the bottom water that is less hot than at the top. I take short showers and never experienced cold water. But the Mrs. says her showers get cold at the end. Not extremely long but longer than mine.

So, testing the lower element and thermostat can be done with a DVM? With power on and calling for heat shouldn’t I get 240volts across the two terminals at the element when it is heating? And, if bad I get nothing? No volts means either the element is bad or the thermostat is not sending power to the element? Which could be no heat required or a bad thermostat? Or, do I disconnect the wires to the element and just check for continuity across the element?
 
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Old 12-28-18, 09:30 AM
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A electric water heater only turns on one element at a time. Power enters the top thermostat. When the upper layer of water is cool the thermostat closes sending power to the upper heating element. Once the top layer of water reaches the set temperature the upper thermostat turns off the upper element and sends 240 VAC to the lower thermostat. If the lower thermostat then turns on the lower element as needed.

Since the upper thermostat and element get the most use they more frequently fail. I start diagnosing at the top and work my way down. First I leave the heater powered/energized and test for 240 VAC out to the element. Then I turn the upper thermostat down and check to see if the upper thermostat is sending power to the lower thermostat. Then check to see if the lower thermostat is sending power to the lower heating element. If that's all OK then I turn off power to the heater.

I set my meter to check for continuity. Remove the wires from the heating elements. Test for continuity between the two screws. There should be continuity between the two screws. If not the element is burned out. Next test each screw to the metal base of the element. There should be NO continuity from either screw to the base. If there is the element is shorting out and needs to be replaced.
 
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Old 12-28-18, 10:24 AM
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Thanks for the detailed info. Looks like all is working as designed. Get 240 to upper, then to lower. Tested both elements without power with wires removed and both have continuity. And neither shorted to tank. Rats! Means I just don’t get enough hot water due to tank size and wattage. It is 30 gallons and 3500 watts. Looks like a 40 gallon 5500 watt tank is in our future. Largest I’ve found that is not over 20” diameter, all the space we have.
 
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Old 12-28-18, 11:45 AM
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We are on a municipal water system. Do I need to also install an expansion tank on the supply side? The current water heater does not have one. Nor the house water system.
 

Last edited by jeweler; 12-28-18 at 01:15 PM. Reason: Clarity
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Old 12-28-18, 01:29 PM
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Any water system with a water heater should have an expansion tank.

The best location is in the cold water inlet to the heater with no valve or check valve in between.

The pressure tank of a well supplied system will double as the expansion tank proviced that no valve in between is closed.
 
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Old 12-28-18, 01:46 PM
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New house to us, but nearly 20 years old.
How old is the tank? If it's 10 or more years old, you need a new one.
 
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Old 12-28-18, 02:06 PM
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Agreed. That is the jist of this thread. We are replacing the tank and asked whether we needed to also install an expansion tank with the new hot water heater.
 
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Old 12-28-18, 02:11 PM
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Allen says an expansion tank should be used. I have seldom seen an expansion tank with a hot water tank. But I'm not a plumber and I don't see where it can do any harm.
 
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Old 12-28-18, 02:30 PM
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Necessary or just not harmful

I am not trying to make additional work at additional expense. Is an expansion tank necessary?
 
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Old 12-28-18, 02:34 PM
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I would say not. I don't have one, and any of the units I installed over the years never did, but I only installed one electric tank, the rest being natural gas. But if Allen or any of the experts want to chime in, please do. If a boiler for a heating unit is involved, then yes an expansion tank is needed.
 

Last edited by Norm201; 12-28-18 at 03:30 PM.
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Old 12-28-18, 07:13 PM
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I am not addressing code issues, but just if you NEED one. If you have a closed system, meaning if there is a check valve in the system, you NEED an expansion tank. Some pressure reducing valves and some replacement water meters now have a check valve. I didn't NEED an expansion tank for many years, but since my last water meter change I now NEED an expansion tank.
 
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Old 12-29-18, 05:23 AM
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Every new tankful of water will expand when heated. In some systems the expansion results in pushback into the city water main so the desirability of an expansion tank is not obvious. Use of hot or cold water or even a leaky faucet can relieve the pressure from the expanding water so as to not trip the water heater relief valve.
 
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Old 12-29-18, 05:29 AM
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If you have a closed system, meaning if there is a check valve in the system, you NEED an expansion tank.

Like Joe said, it depends on where you live. In our little city homes have no meters so we have an open system. When the heater comes on and builds pressure it just goes back toward the street,... open system.

City keeps the pressure around 60# so we don't need those valves that controls the pressure, name escapes me this early.


Edit: Al types faster than I do.
 
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Old 12-29-18, 06:12 AM
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We are located near the ocean in NC. There are backflow preventers for the irrigation systems in everyone’s yard. They are removed in the wintertime to prevent freezing. They are outside near the street and water meter. I would assume this means the household Water does not have one. Does that follow? Or would there also be something separate for the house as well? The backflow preventer is pretty large. I know there is not another one in or under the house. But, could there be a small check valve going into the house? What would I be looking for?

I called the county building department to see if a permit was required for the replacement water heater and was told no. That suggests they are not now requiring an expansion tank. I would have expected they would have told me then if one was required. Besides protecting the house plumbing from excess pressure isn’t this also a device that prevents household water from flowing back into the city supply? If they installed these at the water meter wouldn’t that preclude the need for a backflow preventer for the irrigation systems?
 
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Old 12-29-18, 07:09 AM
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OT: The backflow preventer at the garden hose bibb keeps possibly contaminated water from backing up into your house and going to your faucets. The backflow preventer at your water meter keeps possibly contaminated water from backing up into the water main and going to other people's faucets.
 
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Old 12-29-18, 07:18 AM
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I believe ours is to protect the municipal water supply. Once it is removed for the winter the household water is not affected but the irrigation supply is cut off. This seems to reinforce my idea that the municipal supply does not have a check valve at each home's water meter.
 
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Old 12-29-18, 12:40 PM
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Every area I've seen homes do NOT have back flow preventers on the water main. Backflow preventers are required on irrigation lines since they are open ended to the dirt and contaminates.

I put expansion tanks in the same category as Pressure Reducing Valves (PRV) and arc fault circuit breakers. Homes worked fine for a hundred years without them, but they are now required. The situations they are designed to protect against are extremely rare... which is why things were fine for so long without them. But, there are situations where they are beneficial, just not everywhere.
 
 

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