warm water coming from cold faucets

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mk617435

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This mystery has been happening for 2-4 months without ANY reason. When cold faucet is opened anywhere in the house, warm to very warm (~120degF - ?) flows for the first, say, 30 seconds (or longer). It happens after long period of rest (first thing in the morning, for example). Room temperature water has always been coming out of cold faucet...until now
No plumbing/electrical work has been done recently in the house. Somebody/something is heating cold water pipes in the walls.
Can anybody give a clue, please? I am gong nuts... 🤔
 

Helper Dave

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This is usually caused by a leak through a single handle faucet. Showers are a big culprit, or a single handle kitchen, or bathroom sink.

You generally just have to replace the cartridge inside, and then you're all fixed up. It's just an internal leak, so it's not something you'd see, per se.
 

arctic bill

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some times there is a cross over or by pass, this is where the hot and cold and connected and when you turn on the hot you create a lower pressure and the cold crosses over to the hot side diluting the temp to warm, Some one needs to check every connections in the house. some times in the garage there is hose that looks like this 1633979835459.png
 

mk617435

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This is usually caused by a leak through a single handle faucet. Showers are a big culprit, or a single handle kitchen, or bathroom sink.

You generally just have to replace the cartridge inside, and then you're all fixed up. It's just an internal leak, so it's not something you'd see, per se.
Thank you for the reply. I do not think it is the case for following reasons:
There is only one single handle faucet in the house on 2nd floor and I observe this weirdness in two faucets upstream (1st floor)
If there is a leak, hot water line pressure should be higher than cold water - not likely as I have tankless heater.
I am considering (harebrained) idea of tasteless/colorless contamination reacting with water - ??? heating (and keeping warm) pipe full of water should take some energy.....
 

SHEPLMBR

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Thank you for the reply. I do not think it is the case for following reasons:
There is only one single handle faucet in the house on 2nd floor and I observe this weirdness in two faucets upstream (1st floor)
If there is a leak, hot water line pressure should be higher than cold water - not likely as I have tankless heater.
I am considering (harebrained) idea of tasteless/colorless contamination reacting with water - ??? heating (and keeping warm) pipe full of water should take some energy.....
It only takes 1 faucet for a cross over
 

mk617435

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I have a tankless heater with the valve cutoff on the cold side. I closed it, water was flowing out of hot faucet (waited for ~30 seconds). Bingo! Thank you!!!
:):):):)
 

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