Quick Answer:
If the main shutoff jams partway so water still flows, don’t panic. First try simple, careful fixes: loosen the packing nut slightly, make small back-and-forth movements of the valve stem (cycle micro-movements), then restore packing tension. If the valve still won’t move or you see active leaking, stop and call a plumber.
Why This Happens
- Mineral buildup or corrosion on the stem or gate can lock the mechanism partway.
- A packing nut that’s been overtightened can bind the stem and stop full travel.
- Internal parts—like the gate or seat—can seize or break from age and stress.
- Debris in the line or a bent stem can allow partial flow but prevent full open or close.
Step-by-Step What to Do
Prepare and assess
- Wear gloves and have towels or a bucket ready for drips.
- Locate any secondary isolation valves (street or curb shutoffs) and note their position.
- Check for signs of active leaking before you touch the valve; if water is spraying, stop and call a pro.
Loosen the packing nut slightly
- Use an appropriately sized wrench to back off the packing nut 1/8 to 1/4 turn. The goal is to relieve friction on the stem without making it loose enough to leak.
- If the nut is badly corroded, apply a small amount of penetrating oil and let it sit a few minutes before trying.
Cycle micro-movements
- Use short, gentle strokes: push the stem a tiny amount toward full open, then back toward closed. Repeat slowly to work mineral deposits free.
- A small back-and-forth action (micro-movements) is safer than long forceful turns. Don’t try to power it past a hard stop.
Restore packing tension
- When the stem moves freely again, tighten the packing nut just enough to stop minor leaks—usually the reverse of how you loosened it.
- Operate the valve once or twice to confirm smooth travel and then recheck the nut for slight snugness.
Test carefully
- Move the valve to fully open and fully closed positions slowly to confirm full travel.
- If you see leaks around the stem, tighten the packing nut in 1/8-turn increments until the leak stops, without over-tightening.
- If it won’t reach full positions or starts leaking badly, stop and contact a professional.
For related issues, read about Main shutoff won’t reopen after being closed and Main shutoff valve spins freely but does nothing.
What Not to Do
- Do not force past resistance or you may snap gate.
- Do not strike the valve with a hammer or use excessive leverage; this can break the stem or internal parts.
- Do not remove the packing completely unless you are prepared to replace packing and reseal the stem.
- Do not work on the valve if active spraying would cause a flood or electrical hazard—shut off other supplies and call for help.
When to Call a Professional
- Water continues to flow and you cannot get the valve to a full open or closed position after trying the steps above.
- You see active leaks around the valve body or stem that worsen when you touch the packing nut.
- The valve is old, corroded, or located where a failure would cause major damage (basement, mechanical room).
- You don’t have access to an alternate shutoff and a reliable isolation is needed immediately.
Safety Notes
- Work slowly and keep hands clear of potential spray paths; sudden breaks can cause high-pressure leaks.
- Use eye protection when applying penetrating oil or when working on corroded parts.
- If pipes are frozen or pipes are lead, avoid aggressive mechanical action and call a professional.
- If you’re unsure whether the valve is the only control point, stop and get professional help to avoid unexpected flooding.
Common Homeowner Questions
- Can I replace the packing myself? Yes, if you’re comfortable with basic plumbing work; replace with correct packing material and test for leaks.
- Will lubricating the stem fix it permanently? Lubrication can free a stuck valve temporarily, but corroded or worn parts may require replacement.
- Is it okay to leave the valve partially open until a plumber arrives? Not usually—partial positions can worsen damage and leak; try the gentle steps above, then isolate and call a pro if it won’t move fully.