Without having a stop in the run you'll have to turn off the system, unless...If it is the hot water side you can turn it off at the water heater.
It is not recommended to replace a shut off valve without turning off the water supply. Turning off the water is necessary to prevent leaks and ensure safety during the replacement process.
It is not recommended to drain a water heater without turning it off first. Turning off the power or gas supply to the water heater is important for safety reasons to prevent accidents or damage to the unit. It is best to follow the manufacturer's instructions for draining the water heater properly.
Isolate it from the water supply then replace the defective valve
It means to shut off the water feed to the washing machine.
The process for toilet supply line replacement involves turning off the water supply, disconnecting the old supply line, installing a new supply line, and then turning the water supply back on to check for leaks.
Stop Valve Key
It is not recommended to fix a leaking pipe without turning off the water. Turning off the water is the safest and most effective way to prevent further damage and ensure a successful repair. If you attempt to fix the leak without turning off the water, you risk causing more damage and potentially making the situation worse. It is best to turn off the water supply before attempting any repairs on a leaking pipe.
Cold feed
primary flow
never
primary return
Cold feed