No hot water in 1 bathroom and kitchen, but Ok in other places

[ilya]

Hello all,
just bought new house (3 yo), 2 stores. I got gas heater on the second floor in the attic. I have 3.5 bathrooms and in the master (1 st floor) and in one of the kids bathroom (2nd floor) hot water is ok, approx 1 min to get really hot.
But in the kitchen (1st floor) and another kids bathroom (2nd floor) hot water is kind warm, but not hot. I run it for 20 min, same warm. I opened all facets, showers, no luck. I closed cold water supply in the "problems" places, and open hot water: same not hot just warm. Any ideas what could be the problem? air trap? something else?
Thanks for help
Ilya
PS house in Dallas area. and i think all pipes are plastic.

 

[Beni]

OH Joy, sounds like you have a cross connection somewhere. Good call on closing the cold water valves at the fixtures, BTW...

Do you happen to have a hand sprayer on a kitchen sink with its own On-off valve on the sprayer. One of the fancy ones with a tall U bend up from the deck faucet. Used on better homes sometimes. If so then close the faucet valves after each use.

If not life gets a little more interesting.

When pressure testing the water system after rough in, the hot and cold is tied together, many times at the water heater. But sometimes somewhere else. Sometimes that cross connect is forgotten about.

If you have a pipe that comes out of a wall and goes back into it, that could be it. Though it could be buried in the wall somewhere too. Maybe around the kitchen area on the first floor.

 

[AQualityPlumber]

I have ran into a similar situation before. The cause was a failed spring check valve on the recirculation pump for the hot system. The system worked correct when the recirc pump was running because it was pushing the water. However when the timer on the pump turned off and you use a fixture it would siffon the cold back through the check valve. Creating the allusion that the hot and cold were crossed when in fact is was a check valve stuck open. This scenario is a possibility if you have a recirculation system installed on the hot, typically installed at the hot water tank.

 

[IFIXH20]

Ilya, The kids bath that has hot water is it over the master bath and the bath that does not have hot water, is it over the kitchen, If so ,I am wondering do you have two water heaters. Turn the water valve above the water heater ( in the attic) off, check all fixtures for water pressure on the hot side only, If you have water presssure at some of your fixtures, then you have another water heater somewhere in your home.