wierd situation

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OK Guys,
Here's one that's got me puzzled. It's in a one bath, one kitchen apartment that has it's own WH. The bathroom was piped by the former owner, so anything is possible (it's the same place that almost killed me two months ago). All the faucets are two handle, and there's no laundry.
The problem is that the cold water never gets cold. It's always lukewarm or hot. I thought it'd to be a simple cross connection somewhere, but it's more complicated. Here's what happens. When I go to the WH, and hold the pipes when the hot is run, the cold inlet gets cold, and the hot outlet gets hot (which is normal of course). But when the cold is run, the hot water backs through the WH, making the cold inlet get hot.
So what could make hot water come backwards through the cold inlet, and then throughout the rest of the cold system?
The only way I can think to fix it is to put a check valve in the cold inlet, but it doesn't ease my mind any.
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Hi Mike, A few questions:
1. Is there a hot water return system of any kind? 2. What is the routing of the CW service? 3. Is there any possibility of a cross-apartment cross connection? 4. Have you checked the dip tube? 5. Have you shut down the cold side of the water heater and confirmed that the cw entry is on the right side and that all the hot side openings are dead?
Please answer each question to the best of your ability.
Bob Wheatley
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Mike Grooms wrote:

Any chance someone hid an expansion tank on the hot side of the WH and its pushing water back when system pressure drops while a cold faucet is open? (A very WAG, I know...)
Jeff
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Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)
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sounds like a cross connection caused by a bad tempering valve on a toilet or something like that. when givin equal pressure drop hot will fight its way to front of line.

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Mike Grooms wrote:

I'd suspect the happy homeowner piped cold to hot under the bathroom. Because of different hot/cold pressure drops in the piping this could work out just as you describe. Water will take the path of least resistance. This could mean that all the hot comes through the water heater undiluted by cold but open a cold faucet and half the water comes backwards through the water heater from the cross connection.
MM
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try to isolate the toilet if you can't get to the pipes, otherwise crawl under near toilet and look for tempering valve. id start by looking at all my tempering valves.

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Guys,
I'm sure it'll make sense when I finally figure it out. There must be a cross connection somehow-somewhere. There's no laundry, nor tempering valve, nor single handle faucets. It's city water, and not a well, meaning the pressure is consistent and strong. I think the dip tube is OK, since there's sufficient hot water available.
What I find really confusing is that the water is backing through the water heater when running the cold, and yet when the hot is used it's not affected. I'll let you know when I solve it. Thanks for the suggestions.
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what about the shower valve isn't it a tempering valve?? last time this happen to be it was a becon valve hidden in floor under toilet.

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"Ned Flanders"
The shower valve is a two handle valve, so a cross connection couldn't happen without me knowing it. I also checked the toilet, and I can tell by the layout and visible pipes that there's no tempering valve.
The former owner piped in a new shower and sink. It's probably in there somewhere.
I'm not sure if I'm going to start tearing walls out, or if I'll just put a check valve on the WH.
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Mike Grooms wrote:

Shut the cold valve on the water heater and then turn on each hot tap in turn to see if any cold comes through the suspected mystery cross-connection.
MM
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"Mark Monson" <

I already did that, and the hot seems normal. See why I'm a little stumped!
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is there a washing machine?? it is rare but a stuck solenoid can cause this.

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"Ned Flanders"
There's no laundry, which was one of the first things I thought of. I'm pretty sure it's that some moron just connected a cold to a hot when the bathroom was remodeled. The backing through the WH is what's confusing. The reason I'm surprised is that I'd think that when, for example, the cold is turned on in the kitchen, that there'd still be pressure on the cold side of the WH that'd be pushing in opposition to the hot. It's wierd.
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draw it out on paper and pretend you have a vacuum cleaner on the end of every supply. follow the easiest path to water heater if you draw a cross connection. remember the hot is going to be higher pressure than the cold so it will go first. The kitchen sink being weird I assume means the sinks cold supply is next to the incoming water which is high pressure. you would think that cold would just zip right out the cold faucet. However at the tee where your water main comes in will have slightly greater pressure on the downstream side pushing back against the water main; so when you turn on the sinks cold it sucks from the downstream side of the tee not the incoming main, which could cause reverse flow in the wh caused by venturi effect. the tee where you have the cross connection becomes the new water main for the cold supply to the house because it is the opening to the cold system with the highest pressure. On city water i install a check valve on the cold supply to wh then a thermal expansion tank.

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"Ned Flanders"
Some of us have mentioned that the hot water will have more pressure than the cold. If there's no check valve on the WH, why would this be true. It doesn't make sense to me.
Mike
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Just because there's no check valve does not mean that the pressure is not still being created. It just gets pushed back up into the cold side. The hot side is a closed system so it cannot acept "anything" as long as the fixtures are not in use.
Bob Wheatley
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the expansion starts there so does the pressure.

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"Ned Flanders" <
I just wonder, really, how much actual water will push back through the cold from the WH. I can't imagine it being more than just a little.
The new suspect is that the apartment shares a wall in common with another apartment. I'll do a little tearing apart and let everyone know.
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So the water never gets cold. You've compared this to the water temp coming out of the city supply so you know it could be cold right. And this happens under static (no flow) conditions. Shouldn't have any gravity fed convection unless there is a cross connection and you ruled that out already.
Maybe the cold pipe is being heated by a source other than injection of heated water. Does the pipe run through a hot space (like an attic) or a heat sink (concrete slab or wall exposed to direct sunlight) or is it directly in contact with the hot pipe or another warm surface?
I bet on an unintentional solar heat sink.
Just my thoughts. (If it don't look like a duck, maybe it really isn't a duck)

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More to add....
When did the owner do the add on plumbing? Was it after last winter? If I am right about an unintentional solar collector, the pipe will be susceptable to freezing this winter. If the problem is seasonal, this also supports my idea. Add the check valve (since it is eaier than the alternatives), if it doesn't improve significantly you may be back in December.

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