How to Loosen a Stuck Threaded Pipe Union
Plumbing that has not been disturbed since it was installed. It prefers it that way.
Unions and threaded fittings on old galvanized water pipe rust solid. The key is a backup wrench so the force goes into the fitting and not into the rest of the pipe run.
Step by Step
- 1
Confirm what the pipe carries
If it is a gas line, stop. Gas work is for a licensed professional.
- 2
Shut off and drain
Turn off the water and open a faucet below the work to drain the line.
- 3
Soak the threads
Spray the union nut threads and the joints on either side. Give it time.
- 4
Two wrenches
Hold one side of the union with a pipe wrench and turn the union nut with another. The jaws should face the direction of turn.
- 5
Clean and re-seal
Clean the threads and the seat. Use new thread sealant appropriate for potable water.
No torch on threaded pipe in a house. Never heat a gas line. On water lines, heat risks the solder joints and anything flammable behind the wall.
- Never use penetrant on gas lines and never work on gas lines yourself.
- Flush the line well after work so no penetrant stays in drinking water.
Which Penetrant, and Why
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Common Mistakes
Using one wrench and cracking a joint further down the line.