Hi,
I installed Moen L82839 tub/shower valve in the basement a month ago and have got the problem with it.
When I turn on the valve 20-30 degrees counter clock wise, warm water comes out from the bathtub faucet. I think it should be cold water up to 90 degrees. I've already tried to replace the cartridge and still have the same problem. Can it be related to water pressure? I used PEX pipes for the hot/water lines and the riser for shower head, and used copper pipe only for the shower faucet. I have water heater in the basement. I welcome any idea...
Thanks in advance.

Did you reverse the hot and cold supplies?

I should add some more to clarify my problem.
After about 50 degrees, gradually cool water comes out because I think cool water is dorminant after passing the certain point. I would say it works normally after that certain point.
Refer to the added picture for the point where warm water comes out.

Hi EPMiller,
Thanks for your help, but my problem isn't simple like that. I didn't reverse the water supply lines and tried to install the cartridge upside down. It made the valve work totally the other way: hot water first and then cool water.
L82839 valve consists of mainly the valve body and the cartridge. As I tried to replace the cartridge, I suspect water pressure; otherwise L82839 is designed to work that strange way.

Did you run the hot and cold lines close together down in the wall? Or can the cold line get warm in a heat duct?

Just some guesses. GTG

Hi,
I don't think it has to do with running lines.
I tested the vavle again and should say it is hot water rather than warm water. By 30 degrees rotation, hot water comes out of spout, and then warm water starts to run at 45 degrees. So, I'm going to install the shut-off valve on hot water line and test it again to figure out it is related to water pressure. In the meantime, I really wonder anyone who uses MOEN L82839 didn't experience the same problem.
If the shut-off valve doesn't work, my choices are using it as it is or replacing it with the two handle model.

Thanks,
Jimmy

Don't install a shutoff valve, just shut off the water heater supply line, relieve the pressure and then see if you get hot water at the Moen valve. I think you have the cartridge reversed. Could the whole unit be installed upside down? I don't have time to research the particular unit, you can do that.