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Old 01-28-2009, 01:45 PM   #1
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hot water check valve?


Hi;
I have a situation in my basement bathroom where I believe cold water is flowing from cold to hot supply across the open tap of the bathtub/shower when I have the shower flow stopped at the shower head (tap remains on).
The problem is that when I am taking a shower, and the washer is filling (constant flow), I have a good water temp in the shower, but after shutting off the flow at the head (to conserve water) and then turning back on, I get only cold water from the shower for about five seconds.

At first, I thought the hot water heater might be going bad. It's 10 years old.
But further testing proves that there is enough hot water.
I have therefore come to the conclusion that the only way cold water can be getting into the hot water supply for the shower is that it is flowing from cold to hot across the open tap of the bathtub while the water flow is shut off at the shower head.
This is happening because the pressure on the hot water supply drops lower than that on the cold water supply, and there is no mechanism to stop that difference in pressure from causing a flow across the open tap.

I could install a completely new bathtub faucet set; one with a pressure equalizing feature, that would stop this action, and also provide a more even water temperature at all times.
This is very expensive and time consuming though.
So, I thought that perhaps I can just install a check valve in the hot water supply for the bathroom. This would be very easy to do. I have access to these supply lines from the furnace room.

Can I purchase such a check valve for a 1/2" pipe?

Thanks

FW

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Old 01-28-2009, 01:53 PM   #2
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hot water check valve?


Why would the pressure on the hot water side drop lower than the cold?

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Old 01-28-2009, 06:45 PM   #3
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hot water check valve?


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Originally Posted by martyshel View Post
Why would the pressure on the hot water side drop lower than the cold?
You know, I don't think I can answer that question<g>.
After I posted, I started to think about it, and it just doesn't make sense. Both hot and cold are fed from the same main, so I cannot understand this.

One might think that my problem is the hot water heater, but then why would hot water return after 5 or so seconds, even while the washer is still filling?
I later found out that the washer was set to cold during this time, so I'm confused.
I went into the furnace room to check it out, and don't see anything amiss. All valves are fully open.

What it seems like to me is that for some reason, the hot water is leaving the bathtub plumbing while the water is shut off at the shower head. This only happens when water is being used in another part of the house.
I'm going to have to do some experimentation, and try to reproduce the problem when I'm not in the shower getting a cold shower<g>

FW
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Old 01-28-2009, 07:06 PM   #4
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hot water check valve?


Let me make sure I am clear here. You have a shower head with a built in shut off valve or some other setup so that you can turn off the shower at the shower head itself, and when you turn off the shower you are shutting it off at the shower head instead of at the faucet, correct?
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Old 01-28-2009, 08:21 PM   #5
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Originally Posted by jporter5333 View Post
Let me make sure I am clear here. You have a shower head with a built in shut off valve or some other setup so that you can turn off the shower at the shower head itself, and when you turn off the shower you are shutting it off at the shower head instead of at the faucet, correct?
Yes. That is exactly the situation. I believe that the issue with the water temp only occurs when the shower is shut off at the head, not when it is turned off normally at the tap.

I had seen this happen in an apartment I lived in. Water pressure was always fluctuating there. The solution was to install a pressure equalizing faucet set.

FW
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Old 01-28-2009, 10:26 PM   #6
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hot water check valve?


OK KE2KB,
The easiest fix is ti shut the water off at the faucet instead of the shower head. By shutting off the water at the shower head you have in effect tied your hot and cold water pipes together. The cold water can backfeed into your hot line or vice versa with this setup. Unless there is a reason not to, just start shutting off the faucet. If there is a need for this set up, then a check valve should help. I suggest a spring loaded soft seat check for this. 2 reasons, springloaded allows you to put the check valve in any position (horizontal or vertical) and it will still close, soft seat keeps it from making a loud bang when it closes.
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Old 01-28-2009, 11:05 PM   #7
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hot water check valve?


Your first diagnosis that cold water is crossing through the shower valve into the hot water supply piping is correct.

That can happen since the resistance to flow through the cold water supply piping is lower than that of the hot water piping, even though the pressures are equal in both pipes. The water heater and it's associated check valves and shut off valves introduce considerable resistance to flow through the hot water supply piping. It very well could be easier for cold water to flow through your shower valve to the washing machine's hot water inlet than for hot water to flow through the hot water heater and associated piping to the washer's hot water inlet. If that's the case, when you shut off the water at the shower head, you very well could have cold water in both supply pipes to your shower valve when you turn the water on again at the shower head.

One way to prove if that's happening is to have someone feel that hot water supply pipe to the shower. If your theory is correct, you should feel the hot water supply pipe to the shower suddenly become cold as it fills with cold water. Have a helper feel that pipe while you shut off the water at the shower head and the washing machine is filling with warm water.

Also, if your washing machine is set on "Whites" so that it fills with hot water only, then that would cause water to be drawn through the shower valve from the cold water supply pipe as well.
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Old 01-30-2009, 01:36 PM   #8
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hot water check valve?


While I think the check-valve would work, I am not going to do anything, since this is an occasional problem; only when the washer is filling or other heavy water use is going on at the same time the shower is being used.
The easiest, and least expensive solution is to shut off the washer when the shower is being used.


FW

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