Water – Problems with crossed hot & cold water lines on shower


My contractor installed a brand new Grohe universal rough-in box, and a Grohe universal pressure balance rough-in valve with diverter. Right after the rough-in box was installed, and before everything else was done, we started experiencing low temperature of the water in the entire house. In addition, cold water will sometimes flow from the hot taps.

We first thought that it was a problem with the water heater and had it inspected. The water heater guy wrote that there is no problem with the water heater, but that hot and cold pipes were crossed somehow and that that needs to be fixed.

My contractor then went and closed the pass thru valve in the rough-in box and explained that the pressure of the cold water was so strong that the cold water was passing though this valve and making its way back into our hot water supply. Closing the valve seems to have resolved the problem with cold water coming out of the hot taps in the rest of the house.

However, when the shower installation was complete with pbv, diverter and the trim, I notice that the trim dial is switched: that cold water is coming from the hot water indicator, and vise versa. I also noticed a significant reduction in pressure of the main shower head in comparison to my original 20 year old shower head that was replaced. Furthermore, I see that if the trim handle is set to the limit of 'Cold', which displays as 'Hot', the water barely drips. On the other hand, if it is set all the way to 'Hot', which displays as 'Cold', there is strong pressure. This does not make sense to me, as I believe the cold water should have the strongest pressure.

So my questions are:

  1. Does this mean that there is a cross connection between the hot and cold pipes?
  2. If that is the case, what kind of problems will it cause?
  3. Is my low pressure related to this crossover?
  4. Should I make the contractor to open the walls and re-connect the pipes to the correct hot and cold connections, or it is ok to leave it as is and go with his suggestion of adjusting the cartridge and just changing the trim to point to the right way?

Best Answer

Demand the manufacturer's instructions so you can review them. Then respectfully insist that the plumber (who you paid to install it correctly) return and make all needed corrections. It's not right for the plumber to expect you to do anything unless you agreed to up front.

He should be correcting the piping if necessary, he should be adjusting the temperature stops, he should be adjusting the cartridge, he should be ensuring the trim is oriented correctly.