How to Replace a Main Shutoff with a Ball Valve

Why this matters

The main shutoff is the valve a homeowner reaches for with water coming through a ceiling. An old gate or globe valve that turns but does not close, or a stem that snaps in the hand, turns a leak into a flood and a flood into an insurance claim. Replacing it is a short job with three ways to go wrong: you cannot get the water off upstream, you cut a pipe that is carrying the house's electrical bond, or you put the water back on so hard that you shake loose scale and a joint you did not touch. This card is the sequence that avoids all three.

The replacement is a full-port ball valve with unions on both sides. Full port, because a standard-port valve's bore is a size smaller than the pipe and the main is the one place every fixture in the house shares the restriction; the IPC, as adopted, also calls for a full-open valve on the water distribution pipe where it enters the building (check the UPC's wording where that code is adopted). Unions, because the next replacement then takes a wrench instead of a torch or a saw.

Safety and isolation, before any cut

Confirm the upstream shutoff holds before you cut anything. That is usually a curb stop at or near the property line, sometimes a meter valve in a pit or basement. Who owns and operates it is a local question: many water utilities forbid anyone but their own staff from operating the curb stop or the meter valves, and some charge for a turn-off. Read Whose Pipe Is It? What the Utility Owns and What You Own, and call the utility if the curb stop is theirs to operate, is buried, or does not turn with a curb key. A curb stop forced with a cheater bar can break below grade, and then the leak is in the street.

Jump the bond before you separate metallic pipe. In many houses the metal water pipe is part of the grounding and bonding system, and the grounding electrode conductor may clamp to the pipe within a few feet of the main valve. Cutting out a section breaks that path. If a fault or stray current is present, the two cut ends can carry voltage between them, and you are the jumper. Before cutting, clamp a bonding jumper across the section you will remove, cable long enough to stay attached while you work (the related NEC rule, in substance, is that the permanent grounding path not depend on equipment that may be removed for repair; NEC section 250.68 in the 2023 edition, as adopted). Test for voltage between the two sides of the planned cut with a meter proven on a known live source before and after, per NFPA 70E Article 120 (current edition). If you read voltage, stop and call an electrician; the bonding fault is theirs to find. A permanent bonding jumper around the new unions, where the bond path runs through this pipe, is part of the job, and in some jurisdictions it is electrical work that an electrician installs.

Lead service lines. If the pipe entering the house is soft gray metal that scratches shiny, treat it as lead. Do not cut, flare or reuse it; the utility's lead-service program governs it, and disturbing it raises lead in the water downstream. Flush the house thoroughly after any work near it.

Steps

1. Close the upstream shutoff and prove it. Close the curb stop or meter valve, then open the lowest tap in the house (a basement laundry tub or hose bib) and the highest one. Flow should taper to nothing within a few minutes as the house drains and stay stopped. A steady trickle that never ends means the upstream valve passes. Stop there: a passing curb stop is the utility's to fix, or you plan a freeze kit or a wet-capable joining method, never a sweat joint against running water.

2. Drain the house. With the high and low taps open, let the system empty. Shut off power to an electric water heater and set a gas heater to pilot or vacation before draining, because an emptied heater that keeps firing damages itself. A draining system pulls air in through the high tap; that air is what you bleed out at the end.

3. Measure the cut. Assemble the new valve and both union ends dry on the bench, and measure end to end. For each end, subtract the depth the pipe goes into it: the solder cup depth, the press fitting's marked insertion depth, or the PEX fitting's barb engagement. The cut-out length is the assembled length minus both insertion depths. Measuring the old valve tells you nothing about the new one. Measuring center to center and allowing for make-up is covered in Measuring Center to Center and Fitting Make-Up.

4. Cut out the old valve. With the jumper attached, cut with a tubing cutter on copper (it leaves a square end; a hacksaw leaves a burr and an out-of-square face that will not seat in a press fitting). Have a bucket and towels under it: the riser between the curb stop and the valve holds water no tap could drain. Ream both ends and deburr the outside.

5. Join by the method the pipe calls for. Which joint goes where is the shop standard in The Joining Method Standard SOP.

• Copper, solder. Take the union nut and the valve body off the tailpiece, sweat only the tailpieces, let them cool, then assemble. Torch heat on a ball valve's seats ruins them. Lead-free solder and flux on potable water. The torch steps are in How to Sweat a Copper Water Joint That Passes First Time. Solder needs a dry pipe; a weeping service line will not take solder, and a bread plug or a press fitting is the answer, not more heat.
• Copper, press. Works on a damp pipe. Mark insertion depth on both pipe ends with the depth gauge, insert to the mark, press with the correct jaw, check the mark is still at the fitting face.
• PEX. By the system's own method and tools; see PEX Installation Procedure Reference.
• Polyethylene service tubing. Brass compression with an insert stiffener in the tube, rated for the service.
• Galvanized. See How to Transition from Galvanized to Copper or PEX.

6. Support the valve. A main valve is turned hard in an emergency. Strap the pipe within a short distance on both sides so a panicked quarter-turn does not wrench a joint. A valve hanging on its own joints will eventually weep at one.

7. Restore slowly and bleed the air. Close all taps except the highest one. Open the new ball valve fully. Then open the curb stop or meter valve slowly, a little at a time, over a minute or more. A curb stop thrown open sends a pressure wave through a house full of air pockets, which slams fixtures and loosens scale into every aerator and cartridge. Let the high tap run until it flows steady with no spitting, then work down through the house tap by tap. Restore the water heater last, only after its hot taps run water with no air, because a heater fired or energized partly empty burns out an element or overheats the tank.

Worked example: a seized gate valve on 3/4 in copper

A 1970s house, 3/4 in copper service entering through the basement wall, a gate valve that turns eight turns and still lets water through. The utility allows owners and contractors to operate the curb stop. Static pressure at the laundry hose bib before work: 68 psi on a gauge.

Isolation. The curb stop closed with a curb key. Laundry tub and upstairs tub opened: flow tapered and stopped within about four minutes and stayed stopped. The grounding electrode conductor clamps to the copper 18 in downstream of the gate valve. Meter across the planned cut: 0.0 V, meter proven on a live receptacle before and after. The jumper went on before the cut, spanning both the section coming out and the bond clamp, so the path from the street side to the clamp never opens:

 street                      |<---- 18 in ---->|   house
 --[curb stop]---||--*-+--[gate]--+-----[bond clamp]--*-->
                 ||  | |<5-1/2 in>|                   |
                 ||  *====== bonding jumper ==========*
                wall        cut out with the gate

The cut. The replacement is a full-port 3/4 in ball valve with press-connect union ends. Assembled on the bench it measures, say, 7-1/4 in end to end, and each press end takes 7/8 in of pipe at its marked depth. Cut-out length: 7-1/4 minus 7/8 minus 7/8, which is 7-1/4 minus 1-3/4, or 5-1/2 in. Check from the other direction: 5-1/2 in of gap plus 7/8 in inserted on each side is 5-1/2 plus 1-3/4, or 7-1/4 in. The old valve came out in a 5-1/2 in section, with about a cup of water from the riser into the bucket.

Joining. The pipe was still damp from the riser, which is why press was the choice. Depth marks on both ends, inserted, pressed, marks still at the fitting faces. Straps on the wall within 6 in of each union. The jumper was left on until a permanent bonding jumper was in place across the valve assembly, as the job's scope with the electrician called for.

Restore. Ball valve open, upstairs tub tap open, curb stop eased open over about a minute. The tub spat air for 40 seconds and then ran clear. Downstairs taps worked through one at a time. Water heater relit after its hot tap ran steady.

Finish test: it closes, and nothing leaks

Closure under pressure. Static back at 68 psi on the hose-bib gauge. Close the new ball valve. Open the laundry tub tap briefly to drop the house to 0 psi, then close it. Watch the gauge for 5 minutes. Pass: it stays at 0 psi. A slow climb back toward 68 psi means the new valve passes, which on a new ball valve usually means debris on the seat from the restore; cycle it a few times with water flowing and retest. In this job the gauge held 0 psi for 5 minutes.

Then open it and check the joints. Valve open, gauge back to 68 psi. Wrap a dry paper towel around each union and joint for 10 minutes; any spot on the towel is a leak a glance misses. Check the handle travels a full quarter turn without hitting the wall or a joist, because a handle that stops short leaves the valve partly open with nobody knowing.

And the customer. Show the owner the valve, which way is closed (handle across the pipe), and put a tag on it. The best main valve in the county is no use to someone who cannot find it in the dark.

References

• NEC 2023 Section 250.68 (grounding electrode connection and effective grounding path), as adopted by your jurisdiction; check the current edition.
• NFPA 70E, Article 120, current edition, for verifying absence of voltage.
• IPC 2021 or UPC 2021, as adopted, for the valve requirement on the water service; the valve maker's installation instructions.
• See related: Whose Pipe Is It? What the Utility Owns and What You Own
• See related: The Joining Method Standard SOP