I just recently installed a symmons full shower system in my home. System came with tub spout, shower head, and mixing valve with built in diverter. When I turn the tub on I get a steady flow out of the shower head. What could be causing this?

Using Pex or CPVC between the valve and spout will cause it.

I did use pex between the valve and spout but everything is already finish drywall and pained. Is there any solution other than replacing the piping?

Not really, if you have access to the piping underneath you could install a pair of ball valves to throttle down the volume to the faucet. That will improve the situation a bit as well as downgrade the performance of the showerhead.

You could remove the shower head and add a smallish inline shutoff valve, then reattach the shower head to it. That way you can shutoff the water going to the shower head when using the tub spout, or turn on the new inline shutoff valve when you want to shower. I've done that a couple of times and it is a fairly easy fix.

that isn't a great solution in my opinion.
reason being.. when someone is finished showering, they might just shut the little added valve at the shower head and just leave the shower valve itself open. without check valves at the main shower valve, the hot is likely to back up into the cold and start a whole new set of problems.
anyway, my response is to change the pex to copper... additionally you can contact symmons at 1 800 SYMMONS to see if they have any ideas ????

What's happening with the pex and cpvc pipe that causes this problem with the shower head?



Edited 2 times.

The internal diameter of pex and CPVC is so small that it restricts the water enough that it backs up and out of the showerhead. The instructions that come with the faucet say not to use either. The higher the water pressure the worse the problem becomes.

No other than just NOT turning the water on to full flow.

Symmons will probably say that he should have read THEIR instructions about NOT doing it.

symmons valve is either full on or off. volume adjustment is done by moving the diverter lever closer to the center in the case of a tub shower valve or moving right to left for a shower only model..

I have a brand new install of Pfister brand also using 1/2 PEX, however the shower head and bath water outlet are on the "head" wall which has a concrete wall behind the 2x4 wood stud wall so the valve was placed on a side wall with access to the back. My question is - can I increase or decrease the length of either PEX so as to eliminate this problem. Not being a plumber I require feedback. For the record - other showers/ baths in the same house were fitted out with PEX by the original builder.