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?
  • Some showerheads have thermal limiters for anti-scald If hot and cold are reversed, thet feature and possibly more won't work. I'd get a manual off the web. Oh, and a common feature of Victorians is a discreet door that lets you access the shower valve from the back, bookcase with false back, etc., highly recommended. Feb 1, 2016 at 8:30
  • ... Yeah, the place I grew up in had those access panels. If my place ever needs work I'll have to add them.
    – keshlam
    May 7, 2016 at 21:30
  • Concerning the pressure, with the taps closed (no water flow) the hot water will have a higher pressure because the boiler heats up the water causing it to expand. The boiler will have a check valve that prevents the water from flowing back into the cold supply, and a pressure relief valve to prevent disaster. However, when the tap is open and water is flowing, the hot water pressure will usually drop lower than the cold water pressure due to the longer path and extra resistance (through the heat exchange, etc..) May 16, 2016 at 23:41
  • 1
    Remove the flow restrictor in your new shower head to get some pressure back. I do that for every shower head I install.
    – Netduke
    Nov 7, 2016 at 15:16

2 Answers 2


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.

  • 2
    You should not expect the same type of water flow from a modern shower head compared to one from 20 years ago. Most modern heads have "water saving" restrictions, causing you to spend twice as long in the shower and actually using more water. Dec 3, 2015 at 3:48

to your points:

1) no - it doesn't mean they are crossed. it is almost impossible to make a cross connection unintentionally. this is so unlikely its almost a guaranteed impossibility.

2) wont harm anything

3) low pressure is probably unrelated, but could be a result of contamination introduced into the pipes when the work was done (solder debris probably gunking something up in the system)

4) without knowing the specific valves, i can say that almost every shower mixing valve can be simply flipped. you just remove the locking collar, remove the valve core, rotate 180 degrees and then reinsert it and then the locking collar. its usually a pretty simple fix so if you want it done, just get him to correct it. if it means tearing everything out, i wouldnt bother.

you could have a faulty valve. if the above doesnt help or solve the problem. just turn off the shutoffs to the shower, have him remvove the valve core and return it for inspection and/or replacement.

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