On the documented U by Moen Smart Shower, Water Savings Mode permits one outlet at a time; selecting another switches between them. That can be expected configuration rather than a failed outlet. Confirm the installed controller, initial setup and selected preset. Keep any required water-saving arrangement intact, and investigate an outlet that still will not run when individually selected.
Confirm which shower controller you have
A digital shower with several outlet buttons is not necessarily intended to run them all together in its installed configuration. Record the controller and valve product, available outlets and what happens when each is selected. This answer concerns the documented U by Moen Smart Shower, not every Moen valve or digital shower brand.
Moen's controller instructions say that Water Savings Mode permits only one outlet at a time. Pressing another outlet changes which one runs. Without that activated mode, the documented controller can turn on additional available outlets. Switching behavior alone therefore does not establish a failed valve or undersized supply.
Check the original setup before changing anything
Moen's Getting Started guide makes this mode part of initial controller setup and says users may want or be required to engage it. Confirm the installer handoff and the requirements applying to this installation before proposing a change. A feature described as optional in general product guidance can still belong in the approved arrangement for a particular job.
Do not disable a required configuration, remove flow restrictions or change hidden installer settings to make several heads run. If the installation record is missing, have the provider establish the permitted setup with the actual documentation.
Low-flow showerhead selection covers the head and valve's operating compatibility. A controller mode does not by itself decide which replacement hardware is suitable.
Separate presets and paused operation
The controller guide says a preset saves the selected temperature and outlets. An unexpected selection when starting a preset can be a saved operating choice rather than proof that an outlet failed. Compare the selected preset with the documented controller behavior before replacing parts.
It also distinguishes turning individual outlets off from using the power button. When all outlets are turned off individually, the system pauses and indicates that state. That is another operating condition, not the same as a dead controller or loss of water supply. Use the actual instructions rather than resetting the system to guess at the cause.
What still needs a hardware investigation?
If an outlet will not deliver when properly selected by itself, or flow or temperature is abnormal, record the behavior and obtain model-specific service. A known savings setting does not prove the outlet, supply or electronic valve works. Do not open the controller or in-wall valve, bridge wiring or bypass protection.
Changing shower temperatures are a separate supply and mixing question. Shower trim compatibility also requires identifying the actual valve; a conventional cartridge procedure should not be transferred to this digital assembly. Keep the confirmed mode, preset and remaining symptom with the service request.