Water hammer at water heater

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Armstrongap

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I have an electric tank water heater. I can hear what sounds like water hammer in the walls behind it. It occurs anywhere from a few seconds to a few minutes apart. Even with no water running and I live alone. This has been happening for about 12-18 months. When I turn off the water going into the water heater it stops immediately. With the water back on, and the breaker open it continues, even after using up all the hot water left in the tank. Any ideas what this could be?
 

LLigetfa

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It might be water boiling inside the HWT. As mineral builds up around the element little pockets form with hotspots were water turns to steam. When the steam exits the pocket, it condenses back to liquid making a popping noise.
 

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It might be water boiling inside the HWT. As mineral builds up around the element little pockets form with hotspots were water turns to steam. When the steam exits the pocket, it condenses back to liquid making a popping noise.

I suspected this as well. Turning off the water heater and using up the hot water still caused it to persist.
 

LLigetfa

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Sorry, I misread where you said turning off the water supply to the water heater stops it. I take back my prognosis.

Have you looked to see if the TPR valve is opening?
 

Armstrongap

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Sorry, I misread where you said turning off the water supply to the water heater stops it. I take back my prognosis.

Have you looked to see if the TPR valve is opening?

it doesn’t appear to be. It’s connected to some pvc that opens onto the floor(with a floor drain). No water or any sign of water under the opening and latch appears to be in place. The knocking sounds like it’s coming from in the walls, much the same as a water hammer. Could it be possible that I’m getting some kind of shockwaves from the pipes leading into my house? I’m guessing they run right up to my hot water heater first usually? Just strange that it stops when I close the valve entering the heater yet it persists when I kill the breaker and use up all the hot water. It seems it is directly related to water pressure or something
 

LLigetfa

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Some municipal water systems have a PRV that sometimes can make noise but that would only happen when there is water flow. If it is only the feed to the HWT that you are turning off and not the feed to the entire home, that suggests there is flow through the water heater.

Even if there is not a PRV, sometimes a toilet fill valve can open under extreme pressure. This sometimes happens when there is a faulty PRV as well but a toilet is not fed hot water. It can also happen with expansion when the water is being heated but that does not fit with your symptoms. You might want to pick up a pressure gauge with garden hose thread and connect it to a hose bib to monitor the pressure when this is happening.
 

Armstrongap

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Some municipal water systems have a PRV that sometimes can make noise but that would only happen when there is water flow. If it is only the feed to the HWT that you are turning off and not the feed to the entire home, that suggests there is flow through the water heater.

Even if there is not a PRV, sometimes a toilet fill valve can open under extreme pressure. This sometimes happens when there is a faulty PRV as well but a toilet is not fed hot water. It can also happen with expansion when the water is being heated but that does not fit with your symptoms. You might want to pick up a pressure gauge with garden hose thread and connect it to a hose bib to monitor the pressure when this is happening.

I picked up a pressure gauge and hooked it up to the hose bib and sure enough, there are jumps in water pressure with nothing running in my house. Looks like the normal pressure sits at around 90-92 psi and it jumps around between that and 100 psi. Do I need to get an arrester and where do you recommend is the best place to install it? I was thinking right after the meter, maybe with a riser to keep the ground from corroding it. If that’s not the solution I would be happy to hear suggestions
 

LLigetfa

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If you have a PRV, then rebuild it. If you don't, get one. By code you are not supposed to have more than 80 PSI.
 

Armstrongap

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If you have a PRV, then rebuild it. If you don't, get one. By code you are not supposed to have more than 80 PSI.

yeah, I don’t think I have one. I’ll get that and install it, I guess right after the meter? If I’m still having hammering issues I’ll add an arrester too. Thanks a lot for your help
 
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