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Hot water in the cold water pipes

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Hot water in the cold water pipes

Old 04-09-14, 05:42 PM
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Hot water in the cold water pipes

I turn on the cold water. It starts normal temp, then gets HOT almost immediately. Full hot temperature, for maybe 10 seconds. Then goes completely cold and stays cold.

Somehow hot water is getting into the cold water pipes.

It has always done this to an extent (new home) but didn't bother me much until we turned the water heater up a bit recently. Previously it was just warm water for a few seconds, now it's full on hot. Plus I would imagine I'm heating the water in our toilets, the fridge, anywhere we have water, and that's not good. So I can't leave the water heater up at the moment.

This happens in all locations, so it seems we're heating all the cold water in our pipes.

One possible culprit I've read about is the regulator (or cartridge, or something?) in a single-handle faucet failing and allowing the hot to escape into the cold. This makes sense. We have only one single-handled faucet which I replaced a month ago with no effect. I can also test for this in that sink by turning off the hot water valve, letting the cold run a while, and seeing if it still warms up. Which it does, so it's not that sink.

The only other regulators I can think of would be in the showers. These are trickier to test. The problem there is that I don't think I can access them in a way to shut off the hot water line. I removed the handle in our master shower and it didn't seem like I could access anything further in without ripping out the shower or cutting into the wall on the side. I'd rather not do that just to test. We have 3 such showers. It does seem like there should be a way to shut off the water to the shower, but I don't know where that would be.

There are also suggestions of water backing up from the water heater into the cold. I'm not sure how to test for this exactly. We have an expansion tank but I'm not sure how that figures in or even which is the input/output of the water heater.

Help me otter plumbers, you're my only hope!

Last edited by Th0r S1mpson; 04-09-14 at 06:11 PM.
Old 04-09-14, 05:46 PM
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Re: Hot water in the cold water pipes

Have you tried peeing in the pipes?
Old 04-09-14, 06:09 PM
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Re: Hot water in the cold water pipes

UPDATE: Peed in the pipes. Only made it warmer.

I checked the expansion tank and it feels cold. So it doesn't seem to be a backup from the hot water heater (I think)
Old 04-09-14, 06:14 PM
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Re: Hot water in the cold water pipes

A warm water toilet sounds kinda nice. Just go with it.
Old 04-09-14, 06:15 PM
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Re: Hot water in the cold water pipes

Seems like maybe I need to replace a cartridge in one of the shower heads (maybe a o-ring?), but how do I test for which one is failed?
Old 04-09-14, 06:15 PM
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Re: Hot water in the cold water pipes

Originally Posted by Th0r S1mpson View Post
Help me otter plumbers, you're my only hope!
Au contraire, mon ami. I bet there are many non-otter plumbers who could help you.
Old 04-09-14, 06:22 PM
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Re: Hot water in the cold water pipes

Originally Posted by LurkerDan View Post
Au contraire, mon ami. I bet there are many non-otter plumbers who could help you.
Yeah, trying to do what I can first because that will be an expensive call. It takes a long time in between tests just to get it to heat back up again.

There must be a way to test a shower valve for this sort of thing. If there were a shutoff to each shower it would be easy to isolate, but I don't think there is.
Old 04-09-14, 06:24 PM
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Re: Hot water in the cold water pipes

I don't see how the hot could go into the cold as it is pressurized on both hot and cold unless you have a leak in the cold water line. I would call a plumber.
Old 04-09-14, 06:31 PM
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Re: Hot water in the cold water pipes

You may have a small demon living in your pipes and heating up your cold water. I would call a priest; preferably one with plumbing experience.
Old 04-09-14, 06:35 PM
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Re: Hot water in the cold water pipes

There was an episode of Ask This Old House not too long ago that featured the same issue. Like you suspect, it was the shower regulator. I think he just swapped out the cartridge in the shower.
Old 04-09-14, 06:41 PM
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Re: Hot water in the cold water pipes

Originally Posted by ernestrp View Post
I don't see how the hot could go into the cold as it is pressurized on both hot and cold unless you have a leak in the cold water line.
There usually isn't equal pressure from both lines, a defective faucet will allow the water to migrate from one side to the other.
Old 04-09-14, 07:15 PM
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Re: Hot water in the cold water pipes

Originally Posted by grenier View Post
There was an episode of Ask This Old House not too long ago that featured the same issue. Like you suspect, it was the shower regulator. I think he just swapped out the cartridge in the shower.
I guess I could do all 3 showers, but it would be nice to isolate. I'm stumped on that though. Maybe if I crank the water heater up and test the faucet closest to each shower I can determine which one heats up the soonest.
Old 04-09-14, 07:19 PM
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Re: Hot water in the cold water pipes

I suggest you start tearing out drywall till you find the problem.
Old 04-09-14, 07:52 PM
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Re: Hot water in the cold water pipes

Originally Posted by funkyryno View Post
I suggest you start tearing out drywall till you find the problem.
That's what I expect a plumber to say.

I've had some bad experiences when it comes to anything that's not entirely straight-forward like snaking a toilet. One reason I haven't called already. They show up and their first thought is "how much money can I get out of this person." That's according to someone I knew who was a contractor. I never had him do anything for me.
Old 04-09-14, 07:52 PM
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Re: Hot water in the cold water pipes

Originally Posted by Th0r S1mpson View Post
Yeah, trying to do what I can first because that will be an expensive call. It takes a long time in between tests just to get it to heat back up again.

There must be a way to test a shower valve for this sort of thing. If there were a shutoff to each shower it would be easy to isolate, but I don't think there is.
Can you check the wall behind the shower? Some builders put access panels to the cut-offs. Also do you have a circulating pump for your hot water? Turn it off and see what happens. If this is happening at all water faucets (bathroom, kitchen, tub, etc..) there is something going on with the pipes. While you are at it check the water meter to make sure it's not running.
Old 04-09-14, 08:01 PM
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Re: Hot water in the cold water pipes

Originally Posted by Kdogg View Post
Can you check the wall behind the shower? Some builders put access panels to the cut-offs. Also do you have a circulating pump for your hot water? Turn it off and see what happens. If this is happening at all water faucets (bathroom, kitchen, tub, etc..) there is something going on with the pipes. While you are at it check the water meter to make sure it's not running.
No circulating pump that I'm aware of. No access panel (I think there is one for the tub, not not any of the showers).

Yes, all faucets throughout the house.

I don't think anything outside the pipes could be heating the cold water pipes enough to get it this hot (some links I found suggested nearby heat ducts, weather, etc). Plus it is clearly impacted by turning up the water heater. Almost not noticeable (just warm) right now, but if I turn it back up it will happen. As hot as the hot water for a few seconds... but only on higher heat. Like I said, right now it's just warm.

But without a circulating pump, that behavior seems a little weird too if it were simply a valve. Heating the entire line?
Old 04-09-14, 08:26 PM
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Re: Hot water in the cold water pipes

I just changed the cartridge in my shower (the old one was leaking). In the instructions that came with the cartridge there was a section about hot/cold water swapping.

“My hot and cold are reversed…How do I fix this?”

Reversing Hot and Cold for 1225 Cartridge

If hot and cold are reversed, disassemble faucet until cartridge stem is reached.

Using pliers, rotate cartridge stem 180 degrees and then reassemble.
That's for a MOEN shower but thought it might help ...

So turn everything in your house 180 degrees and it should fix your problem.
Old 04-09-14, 10:23 PM
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Re: Hot water in the cold water pipes

Doesn't that just mean the hot setting would put out cold water and the cold would be hot? It's not functioning like that... Turning it to hot gets a hot shower and cold is cold, except the first several seconds.
Old 04-09-14, 10:58 PM
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Re: Hot water in the cold water pipes

This has happened to one faucet in my home. Does it damage anything if it doesn't get fixed?
Old 04-09-14, 11:30 PM
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Re: Hot water in the cold water pipes

I got concerned when I started to notice the freezer and fridge having issues. Hot water in the ice maker and cold water filter probably isn't a good thing. I can't think of any other appliances that would be affected since they use both hot and cold water any way.
Old 04-09-14, 11:42 PM
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Re: Hot water in the cold water pipes

Maybe the hot and cold water pipes are too close to each other somewhere so when there's no cold water running it heats from the hot water pipe for as long as they are near each other? That would explain why it would go from cold, to hot, and then back to cold again. Maybe near the water heater?
Old 04-10-14, 01:17 AM
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Re: Hot water in the cold water pipes

That is my thought too - same as General Zod - hot water & cold water pipes closer than they should be somewhere along the line - if it was my house that would be the first thing I'd be looking into - actually it seems like the thing possible, I mean some of the other theories which have been proposed are just virtually impossible!
Old 04-10-14, 01:19 AM
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Re: Hot water in the cold water pipes

Clearly the problem is the fact that your McDLT plumbing system is no longer functioning. Alan Smithee probably has the parts you need.
Old 04-10-14, 01:55 AM
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Re: Hot water in the cold water pipes

How close is "too close" for the hot and cold pipes? I think the pipes would have to be completely touching somewhere for this much heat to transfer. It's full hot. That would explain the symptoms, but i guess i hope there is a simpler solution than that. Very few pipes are exposed in this house.

Anyone know definitively if it's even possible for hot water to get into the cold pipes through a failed cartridge?

The more I think about this, the more perplexed I am. The hot water heater is in a ground floor garage, and the problem occurs way up on the 3rd floor bathroom, 2nd floor kitchen on the opposite side of the house, etc. That leads me to doubt the cartridge theory since the showers are 3rd floor... and that would mean the cold water is then being heated all the way from there back down to the 2nd floor kitchen? I have no idea how the pipes are run to the various locations but it seems like it would more likely be from the source instead.

I'm going to turn it back up tomorrow and see if I can determine how far down the pipe the hot water goes at various locations. Maybe that will point to something.

Last edited by Th0r S1mpson; 04-10-14 at 02:07 AM.
Old 04-10-14, 02:28 AM
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Re: Hot water in the cold water pipes

Wow, this is uncommon, but I've seen it a few times. The ones I have seen (just twice) both had a spot where the water was actually mixing. One was some home made attempt to do some plumbing where the wrong line was tapped into, and it ended up mixing with the other side, and the other was a clothes washer that had some hook up wrong that allowed for the mixing. In each case, the water started out cold because the water in the pipes didn't move, but once it started, the hot would bleed over to the cold. Leaving it on would just produce warm water.

Look for something like that. If it hasn't been this way forever, then don't worry about needing to get into the walls.

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