Most shutoff valves in a house have not moved since the day they were installed. They sit still for years, and that stillness is the maintenance problem. This walk-through covers how to find each shutoff, how to test it, and who you call when it will not turn.
Find each shutoff before you need it
Walk the house once with a list in hand. Write down the main water shutoff, the valve on the line that feeds the water heater, the stop valve under each sink and behind each toilet, the valve at the washer box, and the gas shutoff at each gas appliance. Note the room and the appliance each one serves. Keep the list with your owner records, wherever you keep the install paperwork.
Check whether each valve is the quarter-turn kind or the multi-turn kind. A quarter-turn valve has a lever that moves a short arc from open to closed. A multi-turn valve has a round handle that takes several full turns. They behave differently when stuck, so know which one you have before you apply force.
Exercise each valve on a schedule
Pick a schedule you will actually keep, such as the start of each season. Move every valve on the list through its full travel. Close it, then open it. Do this slowly. A valve that has sat unused can stick partway, and a hard, quick turn is how a stuck stem breaks.
Watch the stem and the body while you turn. A small drip at the stem or where the handle meets the body usually means the packing or the washer inside needs attention. If the manufacturer or a plumber has said the packing nut can be snugged, snug it a small amount and stop if it does not tighten. Do not keep cranking. A valve that will not hold is a valve to replace, not to force.
After you close a fixture stop, open the faucet it serves and let it run until the flow stops. Then open the valve again. If the valve dribbles while closed, or the faucet keeps running with the stop shut, the valve is not sealing. Write down what you found and the season you found it, and mark that valve for service.
The gas shutoff is a different job
Turn a gas shutoff only if you already know how to do it safely and you know which appliance it feeds. If a gas valve is hard to turn, feels loose, or you smell gas at the stem or a fitting, leave it alone. Call your gas utility or a licensed gas contractor. Do not test a gas valve with a wrench just to see whether it moves. That is a service call, not an owner task.
When a valve needs a professional
Call a licensed plumber when a valve drips after it is closed, when the handle spins without moving the stem, when the body cracks or weeps at a joint, or when a shutoff you need will not close at all. Replacing a valve usually means draining a line, so treat it as work to schedule, not work to rush.
Ask the plumber three things before the work starts. Ask what type of valve they will install and why. Ask whether the line has to be drained, and how long the water will be off. Ask whether the new valve matches the old one or whether nearby pipe needs other changes. Get the answers in writing on the work order.
Keep the list current
Update the list when a valve is replaced, when a new appliance is added, or when a remodel moves a line. Record the install year of any valve you can find, because a valve's age is a planning input like any other system's. If the install year is unknown, write that down too. A current list means the next person who lives in the house can find the main shutoff without searching.
Related guides
If a fixture line feeds a boiler fill valve, the Boiler page lists typical service life and planning notes for that system. For the appliance side of a gas connection, the Gas Furnace page covers planning. Use both as references, not as a substitute for a licensed inspection.