On the documented Rinnai RSC controller, Priority determines which controller can set the water temperature; its light identifies the enabled control. Priority can change only when no hot water is running. The heater supplies one set temperature at a time, so it is not a temperature for each faucet or an anti-scald device. Use the exact heater and controller instructions.
What does the light indicate?
Priority answers which controller has authority to change the heater's temperature. It does not mean that one shower receives priority over another, that heating output increases, or that a safety fault has been cleared. Read the installed heater and controller model before applying a button instruction.
The cited Rinnai RSC SENSEI manual says the Priority button enables a controller when its priority light is off. The orange light indicates that this controller is controlling the temperature. The guide also says priority can change only when no hot water is running.
Record which controller is lit and whether another faucet is using hot water. Do not repeatedly press unrelated service controls or change installer parameters because the desired controller does not respond during use.
One heater setting affects the connected hot-water supply
Rinnai says the heater can deliver water at only one temperature setting at a time. Its operation section explains that connected hot-water sources can provide water at that setting until it is changed at a controller. Priority does not create independent heater temperatures for each room.
Coordinate any setting change with other occupants. Follow the actual heater instructions and the application's temperature requirements; this page does not prescribe a hotter setting to overcome slow delivery or a recirculation fault.
Match the instructions to the controller
Rinnai's current homeowner FAQ lists priority-related temperature control for its MC-601/MC-91-2 controller guidance. The RSC manual provides the specific operation described here. A timer/controller, app or different series can have other controls and operating details.
If the screen is blank, the blank-controller guide addresses a different operating state. If a diagnostic message appears, the Rinnai code overview is the appropriate source for identifying it. Neither condition is resolved simply by transferring priority.
Priority is not scald protection
The RSC manual warns about hot-water burns, particularly for vulnerable occupants. CPSC's tap-water guidance says not to take hot-water temperature for granted and stresses supervision when bathing young children. Use care at the fixture after a setting change.
A controller light or lock cannot substitute for any required temperature-limiting hardware at a shower or other outlet. Water-heater temperature selection covers that wider decision. Keep the intended setting and controller information available, and obtain qualified service for unexplained temperature behavior rather than opening the heater or bypassing a safety control.