this is probably due to improper sizing in your water lines. The lines don't have enough volume to handle everything that's running. Water tries to take the easiest path that it can so if you turn on something that is closer to the water heater or has less bends in the line the hot water will go there. You can increase the line to the tee to a minamum of 3/4".
Put simply, a correctly designed and fitted system does not lose pressure.
I would guess that there is a pinch point somewhere in your system. This allows the pressure to get up to normal when the system is a rest, only to reduce as the water further up the pipe cannot get through the pinch point.
Possibly there are too many bends in the system, each bend reduces the water flow.
If you lose pressure /volume while a faucet is running the cause could be mineral deposits inside the piping. The trouble could be at the hot water tank as many installers forget to install a dieelectric fitting such as a nipple or union
the tap assebly could be cross connected if older shower set
Did you remove the shower head and check for a flow restrictor or mineral deposits blocking the orifices
Its a loss in water pressure to the shower.
family feud answers: shower, take a bath, flush toilet, water plants, wash hands, drink water
Yes, remove your old shower valve and fit a new Moen anti-scald valve. This will not change when other items are turned on.
The valve is not be diverting all the water. This valve may need to be replaced.
The shower valve needs to be repaired! As for the water not shutting off when you turned off the main that is also needing replacement when it shut of by turning on other faucets you were simply diverting the flow from the leaking main shut off.
Outside at the main shut off valve. Showers/Bathtubs do not normally have a shutoff valve like sinks and toilets. The main water valve for the house must be turned off.
Have you got two single faucets or a single lever faucet? It could be a pressure imbalance or it could just need maintenance
On single handle shower valves, designed to let cold water first and turn handle farther to mix hot water to desired setting. If hot water turned on first, possibility of getting scalded. If seperate hot/cold handles for shower, shower valve needs work.
You probably need new gaskets in your faucet.
May be build up in the valve itself or the shower head.