Shower water do not flow when water is running in bathtub

Hello,

In my master bathroom there is a bathtub and a separate shower. When the water is run in both the shower and the tub, the water flow at the shower shuts off completely. Do you have any idea what can be the problem? Could you suggest how to repair this problem?

Thanks in advance for your help!

Regards,
Lu

That's the way it is supposed to work. The water control valve has an opening at the top and bottom. The top goes to the shower and the bottom to the tub. When shower, you close the tub spout so that the water will go up to the shower head. When you use the tub, the water follows the path of least resistance and goes out the spout. There is nothing wrong with you system. You can't run water in both places at the same time.

Luwork said:

a bathtub and a separate shower...

Click to expand...

They either share the same supply lines or the whole house pressure may drop when the tub filler is running. If the flow is not robbed from other areas of the house, then you need only to run separate supply lines to the shower. If it affects the whole house you may need to replumb the whole house assuming an adequate supply to the home.

I guess that you are talking about the shower above the bathtub. But I mean the "separate" shower, which is a walk-in shower with its own glass door. The shower and the bathtub are at the opposit corners of my master bathroom. Is it still true that either of them can flow?

The only possible answer is that you have a "horrible" lack of volume probably, but not necessaarily, caused by very low pressure. The most likely cause is a malfunctioning pressure reducing valve which is limiting the amount of water available in the house.

I would say the most likely culprit is a pressure balancing valve in the shower. If the pipes and/or pressure are marginal, then turning on the tub may trigger the PB in the shower.

IF the PB unit is activating, then it is STILL a volume and/or pressure problem on one side or the other. Volume and pressure are two sides of the same coin. If the pipes cannot supply the necessary volume, the pressure will drop, and if the pressure is too low there will NOT be adequate volume.

I think you just described a conundrum. We don't know nearly enough to make an informed prognosis. The size of the supply lines, the distance, the source pressure, and the flow rate of the tub filler are all factors.

My wife's soaker tub upstairs has full port valves for a fast fill. It can draw the water so fast that the pump hovers below the kick-in pressure precariously close to the low pressure cut-off. That is imposed by the micronizer on the upstream side of the iron filter. The additional flow restriction imposed by the iron filter means that any and all faucets downstairs (without pressure balance spools) slow to a dribble when the tub is filling, using equal portions of hot and cold.

I knew it would be that way when I designed/built the house and plumbed it but to overcome that limitation would have cost more than it was worth.