Quick Answer:
A new bypass or union installed around a smart valve that starts dripping only after the valve cycles usually means the seal didn’t seat properly or the piping is under torsion from the install. Stop the system, dry and mark the leak point (union/O-ring/thread), relieve pressure, re-seat the union and O-ring, tighten evenly, add support to remove pipe stress, then cycle the valve and re-check under pressure.
Why This Happens
When a smart valve cycles it moves parts and slightly shifts connected pipe. If a union or O‑ring wasn’t seated perfectly, that movement can open a small path for water. Misalignment or a stressed pipe turns that tiny gap into a persistent drip. Over‑tightening can distort the rubber seal, and a weak support allows torsion to return every time the valve moves. These problems can also show up alongside other symptoms — for example, a misinstalled valve might make a Smart shutoff installation caused low pressure or stop a local override from working, which links to why a Manual override won’t work in some cases.
Step-by-Step What to Do
1. Prepare and confirm the leak
- Turn the smart valve to idle if it has a manual position. Dry the area around the union and fittings, then place a visible mark (a piece of tape or a pencil line) at the suspected spot to confirm exactly what moves or leaks.
- Note whether the drip is at the union face, O-ring groove, or thread area (union/O-ring/thread).
2. Relieve pressure
- Shut off the nearest upstream supply valve. Open a downstream faucet or bleed line to remove trapped pressure before loosening any connections.
- Confirm no pressure remains by checking gauges or ensuring water flow stops when the downstream point is closed.
3. Disassemble, inspect and re-seat the seal
- Carefully separate the union. Inspect the O-ring for cuts, nicks or distortion. Clean the sealing surfaces and the O-ring groove of debris.
- If the O-ring is damaged, replace it. If it looks in good shape, rub a thin smear of a compatible silicone-based lubricant to help it seat—don’t use petroleum products on rubber.
4. Tighten the union evenly
- Bring the union faces together squarely so the O-ring sits straight. Tighten evenly by hand until snug, then use small, equal increments rather than a single heavy turn. This helps the seal seat without being crushed.
5. Add pipe support to remove torsion
- Install a pipe clamp or strap near the union so the valve and union don’t carry pipe weight or bending forces. Support both sides so cycling doesn’t introduce twist.
- Adjust alignment so the union seats naturally without forcing the pipes.
6. Cycle and re-check under pressure
- Slowly restore supply pressure and watch the marked leak point. Operate the valve through a few cycles and inspect the union, O-ring groove and threads while the system is under normal pressure.
- If a tiny weep appears, tighten a little more evenly and retest. If the leak returns after cycling, recheck alignment and consider replacing the union or O-ring.
What Not to Do
- Don’t overtighten leaking unions—distorted O-rings leak worse after cycling.
- Don’t wrap thread sealant onto O-ring faces or inside an O-ring groove; that hides damage and prevents proper seating.
- Don’t use petroleum-based greases on rubber seals; they degrade the material. Use a silicone or manufacturer-recommended lubricant only.
When to Call a Professional
- If the leak continues after replacing the O-ring and correcting alignment.
- If the union body, valve housing or fittings are cracked or visibly damaged.
- If you can’t safely isolate and depressurize the line, or if the valve is integrated with electrical components you’re not comfortable handling.
Safety Notes
- Always shut off supply and relieve pressure before loosening unions or fittings. Sudden pressurized releases can cause injury and water damage.
- If the smart valve has electrical power, turn off power to avoid activating the valve while you work and to prevent shock when handling wet components.
- Use replacement parts that match the original materials and ratings—wrong parts can fail under pressure.
Common Homeowner Questions
- How long should a reseated union hold? — If seated and supported properly it should stop leaking immediately and remain dry through multiple cycles.
- Can I reuse the old O-ring? — Only if it’s undamaged, clean and pliable; otherwise replace it to be safe.
- Will extra clamps fix a recurring drip? — Proper support often stops leaks caused by torsion, but recurring drips after support usually mean a damaged seal or misaligned fitting that needs replacement.