Quick Answer:
If new leaks appeared after replacing the main shutoff, first stop using water and dry the area. Most post-install leaks come from loose fittings, solder joints that didn’t take, or compression nuts not seated properly. Carefully inspect joints, tighten or re-sweat as needed, and only restore full pressure once you confirm the leak is fixed.
Why This Happens
- Cold joints: soldered connections that didn’t heat long enough or were contaminated can fail once pressure returns.
- Compression fittings: nuts may be loose or the ferrule not aligned, allowing small leaks under pressure.
- Valve faults: a new valve can have a bad packing nut, seat, or handle seal that weeps when pressurized.
- Pipe movement or strain: re-plumbing can shift pipes and create stress at joints, opening tiny gaps.
Step-by-Step What to Do
1. Stop the leak and protect the area
- Shut the replacement valve off if it’s the source, or the temporary upstream source if possible.
- Place buckets and towels under the leak and turn off electricals if water contacts outlets or appliances.
2. Dry and clean for inspection
- Wipe joints dry and look for the exact origin: solder bead, pipe-to-valve connection, compression nut, or packing gland.
- Use a dry tissue or paper towel to trace the leak while someone slowly turns pressure back on so you can see where moisture starts.
3. Identify cold joints
- Look for dull or grainy solder lines instead of a smooth continuous bead—these are signs of cold joints.
- If a joint looks poorly soldered or cracks when touched, it likely needs to be re-sweated.
4. Re-sweat or tighten compression nuts
- For soldered joints: drain the section, clean with emery cloth, flux and reheat until the proper flow of solder creates a full fillet. Only attempt if you have basic soldering experience and safe ventilation.
- For compression fittings: try gently tightening the compression nut a quarter to half turn. If it still leaks, cut the joint apart, inspect or replace the ferrule and reset the nut to the manufacturer’s instructions.
5. Check valve packing and handle area
- Tighten the packing nut a small amount if the leak is around the valve stem; do not overtighten.
- If the leak is at the handle or valve body, note that some repairs require valve replacement rather than a temporary fix.
6. Test under controlled pressure
- Slowly bring water back and watch for any drips for several minutes.
- If repair holds, remove towels and monitor the area over the next day to confirm no slow weeps reappear.
What Not to Do
- Do not ignore slow weeps — small, persistent drips will worsen and can cause water damage or corrosion.
- Do not overtighten fittings or packing nuts; that can deform seats or crush ferrules and make leaks worse.
- Do not operate a valve that you suspect is leaking under high pressure without testing and fixing it first.
When to Call a Professional
- Leaks that continue after tightening or re-sweating, or if the leak is at the valve body, should be evaluated by a plumber.
- If you find a bad solder joint across multiple pipes or inside a wall, call a pro to avoid hidden damage.
- If you notice the situation matches issues described in Main shutoff leaking from handle or you have persistent low flow consistent with Water pressure low after main shutoff replacement, get professional help.
Safety Notes
- Turn off water before cutting or disassembling fittings. Drain the line and open a nearby faucet to relieve pressure.
- When soldering, work in a ventilated area and keep a fire extinguisher handy. Protect nearby surfaces from heat.
- If electrical outlets or appliances are wet, turn off the circuit at the breaker before working nearby.
Common Homeowner Questions
- How long should I watch a repaired joint? Watch closely for at least 30–60 minutes under pressure, then check periodically over 24 hours for slow weeps.
- Can I just tighten a leaking compression nut forever? No. Tightening helps short-term, but a deformed ferrule or misalignment means a proper replacement is the reliable fix.
- Is it safe to re-sweat a joint myself? Only if you have experience with plumbing soldering and proper safety gear; otherwise call a professional.