New Gas Water Heater Temp +30 degrees Possibly Caused by Crossed Plumbing Lines?

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Happee

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Hi, everyone.

This is my first post, so please forgive me if I'm not providing enough information, too much info, or not explaining things clearly. I can unclog drains and turn water lines on and off...that is where my plumbing experience ends. :)

We live in the Twin Cities (MN) and our home was built in 2004. There are four of us living in our home.

In December, we remodeled our basement bathroom and the plumbing company installed a Moen M3330 3-way transfer valve, trim kit, and 2 Moen shower heads. He wasn't super familiar with transfer valves, but it seemed to work out. The transfer valve controls 2 shower heads, one on either side of the shower. We have a small access panel to some of the shower plumbing and transfer valve.

Within a few days, we noticed our 13-year old A.O. Smith Power Vent Water Heater was getting very hot, above 130 degrees. It had always been set just above vacation setting to 120 degrees and we never had any problems previously (always between 116 and 122 degrees). However, we chalked it up to it "getting older" and a regulator having trouble keeping the temperature below 120. By February, the water temperature was 138 and I ordered another water heater, the A.O. Smith G6PVT5050. It was installed on March 25 and set to 120. By the end of the day, the water was almost 150 degrees, so I turned it down to 110 degrees. Two days later, it was almost 140. I let it go for a few days and it was still too hot. I set it to 90 degrees, but then we didn't have hot water for even one shower.

A.O. Smith sent a tech to replace the regulator and it still had the same exact problems: 30 degrees difference in temp from the thermostat setting.

They came again to replace it a second time (that's 3 regulators) on Friday and we still have the same problem. The tech was very thorough. He drained the water heater and, though the hot water was off and there was no water left in the tank, there was still a steady, but small, steam of water coming out through the hose to the drain. We could hear it running behind the transfer valve, despite the valves being off and the hot water being turned off. The other strange thing was that he showed me the 3 hot water lines running into the hot water heater and noted that 2 were warm and 1 felt very cold. He said all 3 should feel at least lukewarm. The one that felt cold runs down into the basement bathroom from our mechanical room, though I can't see where it connects as the cutout is only a 1x1-foot square.

He said that there is something wrong with the plumbing or a faucet somewhere. He then "tested" all the faucets in the house (7 sinks and 3 showers) while the hot water was off. When the faucets were turned to hot, nothing came out. When they were turned to cold, a surge of cold water came out. He said all of them seemed fine and were acting the way they should. However, on the basement shower--which has the transfer valve--turning it to hot brought a continuous trickle of water and turning it to cold brought cold water at very low pressure. He said the problem seems to be with that shower.

I called Moen and the plumbing supply company from which we purchased the valve. Both were surprised by it and both said they can't imagine it's the valve. It seems to be functioning as far as being cold when turned to cold and hot when turned to hot. I don't know if it matters, but we've only used the shower less than 10 times...and only once to take a shower. Otherwise, it's been for about a minute or less to rinse something off. It's rarely used.

The timing of it seems uncanny with the bathroom remodel and we have had the same problem with 2 different water heaters. We haven't done any other remodeling or plumbing changes in the house otherwise, so we are at a loss. I called the plumber's office on Friday and tried to summarize everything. She said she'd have him call me on Monday. I still haven't heard from him. I'm hoping someone on here will be able to weed through my rambling and limited understanding of the issue and know the cause or have suggestions.

Any help you can give is TRULY appreciated. Thank you and I apologize for the length of this post. I wanted to make sure I included everything in case it helps. :)
 
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jadnashua

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Modern shower valves have some kind of anti-scald technology in them, and the most common one is a pressure balance valve. If yours has one of those, typically, unless both the hot and cold were on, you'd get NO water out of it (well, sometimes, it's just a small trickle.

One of the things that can cause a WH to fail to mix the tank's contents well is if there is a constant, very slow leak. That can allow the water to stratify, making the typical temperature sensing not work optimally. Introducing a slow flow of cold water in a WH may cause the burner to turn on to compensate, but without a moderate flow, the water at the top does not mix as well, and it can get hotter than it should. The fix for that is to find the leak (cross-over point), or it could be a low-velocity convective loop.

If your shower valve is using one of the 'transfer' valves (normally called diverter valves) to stop the flow, and you never shut off the main valve, the problem should go away if you shut the actual shower valve off.
 

Happee

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Jim,

Thank you so much for the info.

I don't know if it matters, but we've only used the shower less than 10 times...and only once to take a shower. Otherwise, it's been for about a minute or less to rinse something off. It's rarely used.

When we were testing it (and when we're not using it), the valve is completely closed. Both handles are pushed in. I don't know if that's what you meant by "using one of the transfer valves."

The documentation for it doesn't mention anti-scald technology, though I know most bath sets have it. The valve seemed really simple.

I really hope we don't have a leak. It's just strange that we had no problems whatsoever until the work was done in the basement.

If it's from his installation, I want the plumber to come back to fix it. But it sounds like there's no way to know for sure?

Thanks again.

Modern shower valves have some kind of anti-scald technology in them, and the most common one is a pressure balance valve. If yours has one of those, typically, unless both the hot and cold were on, you'd get NO water out of it (well, sometimes, it's just a small trickle.

One of the things that can cause a WH to fail to mix the tank's contents well is if there is a constant, very slow leak. That can allow the water to stratify, making the typical temperature sensing not work optimally. Introducing a slow flow of cold water in a WH may cause the burner to turn on to compensate, but without a moderate flow, the water at the top does not mix as well, and it can get hotter than it should. The fix for that is to find the leak (cross-over point), or it could be a low-velocity convective loop.

If your shower valve is using one of the 'transfer' valves (normally called diverter valves) to stop the flow, and you never shut off the main valve, the problem should go away if you shut the actual shower valve off.
 

jadnashua

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Someone that posted on the forum had a similar problem when they were using a humidifier plumbed into the hot water supply. Because the flow was fairly small, they had a stratification problem in their WH. This can happen when the flow is slow which doesn't create much mixing. The cold refill water would cause the burner to come on, but the natural convection in the tank was not enough to prevent the water at the top to mix well with the rest of the tank, and it got much hotter there before the aquastat shut the burner down.

There may be other things that could cause your symptoms.

You mentioned not all of the hot pipes were warm...care to elaborate on that or maybe add a picture? That may be a useful 'tell'.

When the WH was replaced or the new plumbing was added, did they change the configuration at the WH?

Do you have a hot water recirculation system? If it's a stratification issue, adding one may solve your problem and provide other benefits. Probably the easiest one to install is one of the RedyTemp units, if you either have or can get a receptacle underneath the vanity sink to plug it in. IT doesn't require any actual plumbing...just relocate the sink's supply lines to it, and then add two new hoses from the unit back to the shutoffs then plug it in. That has enough flow to overcome stratification (I think, you might call them).
 
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