I am replacing my dishwasher and the water supply line shut off valve will not close (won't turn). How can I shut off water so I can replace the dishwasher?

as YOU can not even shut the water, ask the installer YOU should hire

ANY plumber can 'shut the water'

curb stop

meter

whole house shutoff valve

under sink angle valve




replace inoperative valves as / when needed

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

depends on the type valve.
most commonly used valves have a packing nut that can be loosened to free up the stem.
must be re-tightened when you open the valve.

Packy, thats the first Picture I've ever seen were there holding against them self's with another wrench.

Try shutting off the water supply to the water heater, or at the house main shut off. The angle stop can then be repaired/replaced.

"replace inoperative valves as / when needed"

and the ease of this is the full spectrum from novice level to super journeyman pro level.

...... once upon a time in an era long long ago

changed out a 2" cold water supply gate ON THE FLY in a 'downstairs' gang toilet room @ Curtis Wright plant in NJ.


Got wet, almost drowned in 4 FEET of water 'working blind', got 'er done, got paid for the week on Wednesday ... told to return MONDAY.

Yaaaayyyyyyy .... two whole days off

==============================================

"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

You have to consider how old your dishwasher is, and if parts are available can you easily repair it or will you need to hire a repair service.

If the repair will cost close to or more than the cost of buying new, you should probably buy the new unit. Normally, the labor of a service tech is more expensive than the part needed.

If you can still get parts for the old dishwasher, you may want to attempt replacing the part yourself. There are plenty of HOW TO videos on YouTube. Then again, if you do not have the proper tools, you also have to consider the cost of buy the tools needed. In most instances all you will need are normal everyday tools such as wrenches, screwdrivers and pliers. (It is wise for every homeowner to have a basic set of tools. Reasonably priced kits are available at Sears, Home Depot, Lowes, Amazon…).
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elisecoen



Edited 3 times.

I would try what steve suggested and turn off the cold water inlet valve to the water heater, making sure all single handle faucets are in the closed and cold position, and see if that stops the flow to the valve. If that doesn't work then shutdown the whole house main shutoff, if that doesn't work then the curb stop. By that time you might consider calling in a plumber to replace DW valve, WH valve, main shutoff valve.