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How to Diagnose and Repair a Leaking Water Heater

Ask This Old House plumbing and heating expert Richard Trethewey finds a solution for a water heater that recently started leaking.


  1. If there’s a leak at your temperature and pressure relief valve, first test to ensure it’s operating correctly. If it isn’t working properly, replace it.
  2. If the T&P valve is operational, check to see if you have a pressure-reducing valve, usually near the main water shutoff. If a pressure-reducing valve or other form of check valve is present, you’ll need to add a potable expansion tank.
  3. Shut the water off at the water main.
  4. Using a bucket, drain the hot water heater just enough to get below the pipes and the top of the tank.
  5. Use copper pipe and push fittings to connect the expansion tank.
  6. Cut the cold water line above the tank using a pipe cutter, then push both ends of the pipe into both sides of the push T fitting.
  7. Turn the water back on.