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How to Replace a Main Shutoff Valve

Ask This Old House plumbing and heating expert Richard Trethewey shows how to replace a main shutoff valve that is not closing properly


  1. If the indoor shutoff valve is not stopping water flow, the local water department has access to a shutoff valve near the street and can be called to shut off water while work is performed.
  2. With the water off, open the faucets and showers in the building to drain any water left in the pipes.
  3. Use sandpaper to clean the main water line before cutting into it.
  4. Cut into the water line using a tubing cutter. When the line is broken, there may be residual water inside that needs to drain out.
  5. Use the fitting brush to clean the inside of the valve.
  6. Apply flux to the outside of the pipe and the inside of the valve.
  7. Hold the torch to the fitting until the flux bubbles, then touch the solder to the pipe opposite the flame. If it’s the correct temperature, the solder should melt and fill in all gaps.
  8. Call the water utility to turn back on the water.

Ball valves and soldering tools are available at home centers.