Hot water from hose bib when I drain water lines

dlance_2007 · Mar 14, 2011

When I turn off the main house water supply, and then open the adjacent hose bib to drain the water in the lines, I get first much cold water but then I get hot water. I then feel the cold inlet line running into the hot water heater and it is hot. So looks like hot water is being pulled from the tank into the cold inlet line and then out the hose bib.

This sound right?

I can never recall getting hot water out of the hose bib in my other houses. We just bought the place and had a plumber run some new lines for a washer and tub. The fixtures are not installed yet so maybe the plumber made a mistake and has a hot water line somehow connected to a cold line under the house?

Thank you.

SacCity · Mar 14, 2011

When you use the water heater in normal use are the lines appropriate? Hot water outlet hot, and cold water inlet cold, if so then the lines are not crossed.
Assuming that the lines are not crossed the the water from the storage tank is being siphoned out. You may need to put a check valve in the water heater inlet line.

On a recent project there was a second electric water heater in the attic, when draining down the system to make repairs to the plumbing system the electric heating element burned out, and needed to be replaced at my cost. Ouch... and embarrassing...
Michael

Sponsor · 2022-01-29T12:20:58-0800

Terry · Mar 14, 2011

If the plumber roughed in a new tub or shower valve, it may be crossing over there.
Delta makes a plug or cap for their rough-in, and until someone installs the cartridge, it crosses right over.

hj · Mar 15, 2011

Yes, you are siphoning the hot water from the water heater. Usually it does not happen because the dip tube has a "siphon breaker hole" in it, but sometime conditions will negate its function. IF it is an electric water heater, you can drain enough water out of the tank so the upper element can melt and then you will not have any hot water until it is repaired.

Graham Love · Nov 19, 2023

Ive got the same "issue". When I drain the main water line for repairs, it siphons out the gas heated hot water tank.
1) Does it matter?
2). If it does matter, should I install a spring check valve on the cold water inlet side before the expansion tank?

Reach4 · Nov 19, 2023

With a tank WH, it is normal to have a valve on the input water. Is a valve before a tankless not the norm?

Graham Love · Nov 20, 2023

Reach4,
I do have a tank WH. Im wondering if i should put a check valve on to prevent siphoning. Maybe it doesn't matter all that much if some hot water gets sucked out of the tank when I drain the lines.

Fitter30 · Nov 20, 2023

When ever drained down my house in winter water and heater off left all valves open and poured rv antifreeze in toilets and drains. Had only one problem a cracked 11/4" drain valve lost power for two weeks. Crawl space was still at 48°valve was at the outside foundation wall.

Reach4 · Nov 20, 2023

If you close the supply valve to the WH, I expect draining the cold will not siphon water out of the WH.

Fitter30 · Nov 21, 2023

Dip tube has a small hole close to the top the tank to break any siphon.

Cold water dip tube. Antisiphon OR to get the water to...

www.google.com

Graham Love · Nov 21, 2023

Thank you for your responses!

John Gayewski · Nov 22, 2023

It doesn't matter. Just a quark of your system.

Jeff H Young · Nov 24, 2023

Fitter30 said:
Dip tube has a small hole close to the top the tank to break any siphon.

Cold water dip tube. Antisiphon OR to get the water to...

www.google.com

A basic detail I didnt know I dont think this used to be the case As I have had them siphon down pretty far

Hot water from hose bib when I drain water lines

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