Running cold water causes hot water to run out.

[Paul Palmer]

We have a pool that my family is trying to fill up for the season. We run the cold water to fill this pool for around 2-3 hours. This is definitely cold water, because it is running from a spigot outside.

When we start running the water he have plenty of hot water. After running the water to fill the pool and no other water has been used in the house, except for a toilet here or there, the hot water is gone. We test for hot water at different taps and but none. So, we shut off the water to the pool, thinking that could have something to do with this. However, still no hot water.

We leave the water off and don't use the hot water for about an hour. Behold the hot water returns.

I've checked the lines to make sure there isn't some kind of cross connection and there isn't. The only places the cold and hot meet are the hot water tank and the faucets inside the house.

Can anyone provide any clues as to what I should look at and check? I'm stumped on this.

Thank you for any help.

 

[Geofd]

when your filling the pool have someone down at the hwh and see what its doing without any fixtures doing used

 

[Mikey]

Gas or electric WH?

 

[CT18]

Where is the heater located in the house.

 

[JHEARD]

I have seen a hot line supply a hose bibb before. It was a plumbers mistake but it happens. how are you sure this is not the case?