Quick Answer:

If water pressure drops at one fixture or in part of the house, a shutoff valve that is partially closed, damaged, or clogged is a common cause. Start by isolating that valve, inspecting it for visible damage or mineral buildup, and flushing the line. If the valve won’t open or shows clear signs of failure, replace it or call a pro.

Why This Happens

Shutoff valves can cause pressure loss for a few simple reasons:

• Valve partially closed: someone may have turned it without fully opening it again.
• Debris or mineral buildup inside the valve restricts flow.
• Valve hardware is worn or corroded and no longer seats properly.
• Multiple problem points upstream, for example when Multiple valves fail at same time, can lower pressure in unexpected ways.

Step-by-Step What to Do

1. Inspect the valve

• Look at the valve body and handle for obvious damage, leaks, or heavy mineral deposits.
• If it’s a lever, check that the lever is in the fully open position (parallel to the pipe on most valves).
• Note whether the valve stem turns freely or feels stiff.

2. Isolate the supply

• Turn off the main water supply before working on the valve to avoid water damage.
• Open a nearby faucet to relieve pressure and drain water from the line.
• Use a bucket and towels to catch any residual water when you open or remove the valve.

3. Flush debris

• With the valve isolated, remove any removable parts (for serviceable valves) and flush the pipe end into a bucket to clear sediment.
• Turn the main supply back on briefly while holding the pipe open to let debris wash out, then shut it off again to re-inspect.
• If mineral scale is present, gently clean accessible surfaces with a brush or vinegar solution—avoid aggressive tools that could damage sealing surfaces.

4. Replace if needed

• If the valve is cracked, seized, leaks when closed, or still restricts flow after flushing, replace it with a matching type and size.
• Make sure the water is off and the line drained before any removal. Follow manufacturer instructions for soldered, compression, or threaded valves.
• If you’re not comfortable with plumbing work or the valve sits inside a finished wall, consider calling a professional.

What Not to Do

• Do not force the valve. Forcing a stuck valve can break it and cause a sudden, larger leak or pipe damage.
• Do not ignore small leaks. Even a slow leak at the valve will worsen over time and can hide more serious internal problems.
• Do not use excessive heat, power tools, or hammering on a valve inside walls—these actions can cause collateral damage.

When to Call a Professional

Call a plumber if any of the following apply:

• The valve is inside a finished wall or hard-to-reach area.
• The valve is seized and will not move without breaking, or you suspect internal corrosion such as Valve corrosion inside walls.
• Pressure loss persists after you’ve inspected, flushed, and attempted a simple replacement.
• Multiple valves or fixtures show unpredictable pressure behavior or there is active leaking you cannot stop.

Safety Notes

• Always shut off the main water before disassembling or removing a valve.
• Drain pressure by opening a fixture before cutting or removing parts.
• Wear eye protection and gloves when working with plumbing fittings or chemical cleaners.
• If soldering is required, use appropriate fire safety precautions and consider hiring a professional if you lack experience.

Common Homeowner Questions

• Why did the pressure drop suddenly? — A partially closed or clogged shutoff valve is a common cause; follow the inspection and flush steps above.
• Can I replace the valve myself? — Yes if you are comfortable with basic plumbing, but stop and call a pro if the valve is inside a wall or the plumbing uses unfamiliar joints.
• Will cleaning the valve always fix low pressure? — Not always. Cleaning helps if debris or scale is the cause; replace the valve if it’s worn, cracked, or still restricts flow after cleaning.