We just replaced our mixing valve in the upstairs master shower. However, now we are not getting hot water in the upstairs in any of the sinks or showers (it’s getting warm but not hot). Downstairs still has hot water and I’ve confirmed hot and cold lines are to the correct side of the mixing valve (if that makes a difference). Thoughts?

in the offending fixtures, does the water start off hot and then cool down or just never gets hot?

It never gets fully hot

Is the new valve COMPLETELY installed and usable, or is the shower still being constructed?

What brand is the shower valve? Does the shower valve have stops on each side with screw driver slots?

I stand corrected. I took a shower this evening that started out hot and got Luke warm by the end in the fully hot position.

Also, the shower is not fully installed, still under construction. It is a delta mixing valve R10000-UNBX

This may be what is happening .....and where HJ was most likely heading.....

If the cartridge is not installed in the R10000-UNBX valve nor the test plug, you then have open hot & cold water ports. This is allowing a cross connection (mixing of hot & cold water) which results in un-even water tempertures, as you are experiencing.

It has been awhile since I have installed a Delta valve......but they used to come with a test plug.

[www.deltafaucet.com]

You would install test plug in one of the ports to prevent the cross connection.

When you go to install the trim/cartridge you remove test plug and toss it.

If you had the R10000 installed by a plumbing contractor he should have know of this or heaven forbid read the directions.......

Hope this helps.

A PLUMBER knows how to install a Delta valve properly. A "plumber" only knows how to hook it up.