We're in the process of renovating a bathroom and things are pretty close to being done, but we've noticed that that water comes out of the shower head when the tub is being filled. The set up is pretty simple... It starts with a thermostatic shower body (all fixtures by Paini - www.paini.it). The water exits the top of the shower body and then goes down to a tub spout with a diverter. From that point it goes up to a shower head.

When the water is turned on it comes out properly from the tub spout, but after about 30 seconds water starts coming out of the shower head as well. There is a fair amount of water pressure in the building, but we've tried lowering the water pressure by adjusting the shower body and the problem continues.

If I understand things corrrectly gravity is supposed to keep this problem from happening. So what are the things our plumber should be looking for and correcting?

"If I understand things corrrectly gravity is supposed to keep this problem from happening. So what are the things our plumber should be looking for and correcting?"

The output from the shower head is controlled one of two ways. A built in diverter in the valve itself or a spout with a pull up diverter included. From what you tell me you have the latter. When the spouts diverter's pulled up it shuts off the flow to the spout and diverts it tom the shower head. You are correct, with normal pressure, (45 PSI) gravity will prevent the water from entering the shower raiser and leaking out the shower head. However if the water pressure's so great that it sets up a backpressure in the spout it will force water up and out the showerhead. There is nothing wrong with your shower valve. What you need is a PRV, (pressure regulating valve) valve installed on the building supply line or if there is one it needs to be adjusted to a lower pressure.

Good luck, tom

Speedball - thanks for your response, but with the pull up diverter on a spout, there's nothing other than gravity stopping the water from coming out of the shower head prior to the knob being pulled up on the spout. The reason it comes out the tub spout as opposed to the shower head is because it's easier for it to come out of the tub spout.

I took off the spout last night and had a look at it - nothing seems wrong with it.

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Originally Posted by jharper

Speedball - thanks for your response, but with the pull up diverter on a spout, there's nothing other than gravity stopping the water from coming out of the shower head prior to the knob being pulled up on the spout. The reason it comes out the tub spout as opposed to the shower head is because it's easier for it to come out of the tub spout.

I took off the spout last night and had a look at it - nothing seems wrong with it.

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JH, "with the pull up diverter on a spout, there's nothing other than gravity stopping the water from coming out of the shower head prior to the knob being pulled up on the spout. The reason it comes out the tub spout as opposed to the shower head is because it's easier for it to come out of the tub spout."
That's correct. The added head pressure of forcing the water up the shower raiser will direct the flow out the spout simply because it's easier. However that can be overcome with added input pressure. What's the average pressure in your building?
With the spout off did you turn the water back on to see if it came out the shower head?
Regards, tom