Why does my re-plumbed shower come on whenever the tub faucet is opened?

Question

We recently bought this place and are in the middle of updating the bathroom. Bought all new tub/shower fixtures as well as a valve. Handyman installed and flushed/tested/etc. this new valve, and I’ve since installed the new spout, faucet, shower head. Things work okay, EXCEPT when the tub is on, the shower comes on. Not just a trickle!

I’ve searched and searched to find a similar problem with answers in the forum, and what I’ve found is related to pex vs copper and shower height. Everything was copper before and still is. Also, we didn’t change the shower height. I did purchase a gooseneck shower arm to add a little bit of height/length, but it makes no difference. Not knowing much about water pressure, my gut is telling me it’s something to do with that and the new valve. It’s a pressure balancing valve that cost a good $90 and says it’s 20psi (seems low?). It fits the new faucet specifically. The old valve was a delta, and I don’t know if the previous owner had the same problem. We do live in the foothills and have high water pressure naturally. Also, although we have a VERY large and nearly new water heater, we seem to run out of hot water very quickly in the tub. Related?

I have the drywall behind the fixtures open but don’t know where to go with it as of now. Any ideas?

Thanks for reading.

Answer 1

FIXED! The problem was these little buggers inside the shark bites. Don’t know why the handy man use shark bite instead of soldering, but those little plastic bits were restricting the flow enough to shoot everything right up to the shower. Removed them, replaced everything, now the tub works as it should. Holy smokes!

Answer 2

Most valves (all I have seen) meant for tub/shower send everything to the tub by default. The tub has a shutoff, and when you shut tub the water pressure releases out the shower.

So with the limited information that I have right now I will take a guess at your problem. You are getting hot and cold sent to valve. And you have line from valve to tub. I am guessing the line from valve to tub is too small. If you have a valve/system that allows you to change water pressure then let the water run on a very low setting, and everything should go out the tub.

If you do not have a valve system that allows you to change water pressure, then:

1. You should be able to see the first few seconds go out the tub only.
2. You need to restrict your water pressure to your whole house (close your main 80%ish) and then test.

There is a chance that the valve can't spit out water to tub fast enough (highly doubtful but there is a chance). This basically you starting over. So before doing that can you give me the size copper of cold in and hot in and then the size to tub and size to shower?

(also you could be running out of hot water quickly because you have a ton of water period running to this tub/shower)

Answer 3

There are basically two arrangements for diverting water from flowing out of the tub spout and up the shower pipe.

We call one a "spout diverter" arrangement. With this arrangement, the pipe leading to the tub spout from the mixing valve(s) has a tee in the line and is always open to both the tub spout and the shower. The tub spout is equipped with an integrated diverter valve to block flow out of the spout when desired. The water flowing from the mixing valve(s) then has nowhere to go except up the shower pipe and out of the shower head. NOTE: the tub spout diverter valves are generally not designed to be a "tight shot-off", in other words there will always be some water flowing out of the tub spout. ALSO: any other restriction at the end of the tub spout will cause the same diversion of water up the shower pipe and out of the shower head.

The other arrangement , we call "mixing valve diverter". This is where the mixing valve arrangement is equipped with an integrated valve for diverting water to either the tub or shower. The tub spout pipe and the shower riser pipe are not connected at all. The mixer valve arrangement has a seperate port for each, and has a diverter valve mechanism for sending water one way or the other depending on diverter valve position. NOTE: some mixing valve diverters will send water both ways if they are not fully set to one or the other position (or if they are malfunctioning). ALSO: there are many, many (many, many, many) styles and types and each brand and model looks and operates differently.