Cold tap runs hot temporarily

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  #1  
Old 01-25-06, 08:58 AM
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Cold tap runs hot temporarily

I just purchased a home built in 1980. In the 2nd floor bathroom (and only there), the cold taps all run warm to hot for the first 20 seconds or so after being turned on. So, for example, the toilet tank fills with warm water. After this initial period, the tap runs cold as expected.

My first hypothesis was that the cold and hot lines were running together and that the cold pipe was picking up heat from the warm. But this occurs even in the morning when *both* lines should be filled with cool water after cooling overnight. My second hypothesis is that they are running together inside some kind of insulating sleeve.

Possibly related is the fact that the hot and cold supply bibs were reversed under the sink, e.g. the hot was on the right. In replacing the sink faucet set, I just crossed the flexible supply tubes to fix that.

Any thoughts on how to diagnose/correct this without tearing up the walls?
 
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Old 01-25-06, 09:36 AM
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I would agree with your thinking the lines run together and cold is picking up warmth. Unless, the water heater is on the second floor or immediately above the heater. The hot water may be backfeeding up the cold water supply line at the heater. You can check this easily by feeling the cold line at the heater. You may also have a faucet that is crossing over on the inside. A bad washer in a faucet can allow this to happen. Good luck.
 
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Old 01-25-06, 09:40 AM
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Originally Posted by liverotcod
This occurs even in the morning when *both* lines should be filled with cool water after cooling overnight.
And they aren't just running with a heat plenum?


Who inspected this house before you bought it? The inspector should pay to correct this problem.


The answer is that the seller had some work done just before the sale and that work was done incorrectly.

Please read this recent thread about a new water heater.

The solution to the specific case is reported in another thread.
 
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Old 01-25-06, 09:49 AM
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Originally Posted by bolide
And they aren't just running with a heat plenum?
Possible. Very, very possible.

Who inspected this house before you bought it? The inspector should pay to correct this problem.
The answer is that the seller had some work done just before the sale and that work was done incorrectly.
Not in this case, I don't think. The entire system (pipes and heater) are original 1980, located in the basement two floors down and don't appear to have been messed with. The only work I did was to replace the sink faucet set with a new single-handle. That could be the source of the problem except that the tub and the toilet do the same thing. And the basement and first floor plumbing works just fine.

As far as the hot air plenum idea, now that I think about it
the water that comes out of the cold tap at first is considerably warmer than the air in the duct. But since they're both gas-fired, it good be their exhaust stacks causing the problem. I'll check that out tonight. Thanks for your thoughts.
 
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Old 01-25-06, 10:10 AM
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Originally Posted by liverotcod
Possible. Very, very possible.
It doesn't explain the entire toilet tank filling with warm water.




Not in this case, I don't think.
Home sellers in general are sneaky.
Was there no inspection done before purchase?
The reverse hot and cold is easy to detect.



The entire system (pipes and heater) are original 1980, located in the basement two floors down and don't appear to have been messed with.
How do you explain the reversed H and C plumbing?



The only work I did was to replace the sink faucet set with a new single-handle. That could be the source of the problem except that the tub and the toilet do the same thing.
Shut off the water under the sink.
Does the bathtub work correctly?

Shut off the water to the tub also.
Does the toilet get cold only?

Otherwise, somewhere hot and cold are crossed.



As far as the hot air plenum idea, now that I think about it
the water that comes out of the cold tap at first is considerably warmer than the air in the duct.
I see. Well, you don't need to have your water heater so hot. But that does point to an unintentional crossover.

But since they're both gas-fired, it good be their exhaust stacks causing the problem.
No, there really is no way given the volume of water and the timing.


You should follow the procedure I laid out in the other post.

If that doesn't uncover the problem, you can trace your pipes to determine where H and C are crossed. Just leave hot water running slowly in the bathroom and follow the hot pipe. to the point where it splits off for the bathroom. That's where you can uncross the pipes.
 
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Old 01-25-06, 11:31 AM
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Thanks for your help Bolide. I think the home inspector just made sure that the tap ran and didn't leak - I'll check his documentation.

I'll also check out what you have suggested. Thanks again.
 
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Old 01-25-06, 11:59 AM
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I think the home inspector just made sure that the tap ran and didn't leak
He should have checked temperature, odor, and color too.
Something like reversed temperature should have been noted on the report.
Warm water in the toilet could come deliberately from a tempering valve.
But hot water is a no-no.
 
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Old 01-25-06, 02:33 PM
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Hot to cold

Do you have a hot water circulator on your system?
 
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Old 01-29-06, 09:27 PM
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Originally Posted by majakdragon
The hot water may be backfeeding up the cold water supply line at the heater. You can check this easily by feeling the cold line at the heater.
I think this is it. The cold water inlet pipe going into the HWH is very warm where it meets the HWH, and is still warm to the touch at the farthest point I can reach it in the basement, approximately 15 linear feet of pipe. In preparation for working on the bath plumbing, I opened the access panel to the back of the tub, and both the cold and hot pipes are warm at that point. Of course, if you run the cold water for a minute, the pipe (and the water) get cold.

So is this a "replace the HWH" issue? It's on the home warranty, but there's a $100 deductible if I have them come out, so I only want to do that if it's likely that it'll need more than $100 of fix or replacement.
 
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Old 01-29-06, 09:31 PM
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Originally Posted by shacko
Do you have a hot water circulator on your system?
I don't know. Looks pretty straightforward: I can trace the incoming city water through the meter. It then splits to the kitchen cold tap, the outside hose bib, and the water softener. From the softener, it splits into a various cold feeds (these are the problem since I think the pipes themselves are getting heated up by the HWH), going to the three bathrooms etc., and the HWH. After the HWH, the hot pipes likewise split. There don't appear to be any other active components - just valves.
 
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Old 01-29-06, 11:37 PM
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Did you run the problem isolation tests mentioned in reply #5?
 
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Old 01-30-06, 01:01 AM
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Originally Posted by shacko
Do you have a hot water circulator on your system?
??

You may have a circulating pump that mounts under the sink furthest from the water heater.
It connects to the hot line and the cold line valves.
Without this you would need to let the water run for a long time to get hot to the sink.
It appears that it moves the hot water into the cold side and keeps the hot side at an adjustable temperature.
 
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Old 01-30-06, 06:26 AM
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Originally Posted by GWIZ
??

You may have a circulating pump that mounts under the sink furthest from the water heater...
OK, I don't have that.
 
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Old 01-30-06, 06:41 AM
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Originally Posted by bolide
How do you explain the reversed H and C plumbing?
It's not "reversed." It's an artifact of how the pipes are routed from the basement. Normally, the H supply is on the left, and the C on the right. They're the other way around in this installation. I don't think it's relevant to the problem.
Shut off the water under the sink.
Does the bathtub work correctly?
No, the tub supply lines come from the exterior wet wall to the south, whereas the sink come straight up through a partition wall. All pipes coming to the 2nd floor are warm to the touch - warmer nearer the HWH and cooler as you get farther away. When you run cold water, after the pipes are drained of the warm water sitting in them, they run cold as they should. When you run hot water, it starts warm and then heats up, as it should.
Shut off the water to the tub also.
Does the toilet get cold only?
There is no seperate shutoff for the tub.
Otherwise, somewhere hot and cold are crossed.
I don't think it's a crossing issue. As I stated before, my current hypothesis is that it's a problem with the HWH heating the cold water pipes by conduction. I apologize if I haven't defined the problem well enough.
 
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Old 02-04-06, 01:33 PM
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I had a problem similar to this about 7 years ago, getting warm water out of the cold tap. Believe it or not, my "jack of all trades" father-in-law changed the mixing valve on my washing machine, and this fixed the problem. The valve had gone bad, allowing hot water to leak into my cold water supply. It was about $20, and a real easy job.

I know its a stretch - but it worked for me.
 
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