What the test does

After gas piping is installed, extended or repaired, the plumber closes off the system, fills it with air or an inert gas to a test pressure higher than normal operating pressure, and watches a gauge for a required period. If the pressure holds steady, the piping and every joint in it are tight. If it drops, something is leaking.

The test pressure and duration are set by the fuel gas code and the local building department, and can depend on the size and type of system. Rather than relying on a number from the internet, ask the plumber and the inspector what applies to your job.

Where the test fits in a gas job

Before work
Gas is shut off at the appliance valve or meter, and appliances on the affected section are isolated.
During work
Pipe is cut, threaded, joined or replaced; new valves and connectors are fitted.
Rough test
The new or repaired piping is capped and pressurized while it is still exposed, so leaks can be fixed easily.
Inspection
Where a permit is required, the inspector may want to see the gauge holding before walls or trenches are closed.
Restore
Gas is reintroduced, air is purged from the lines, and appliances are relit and checked.

Does your job call for a pressure test?

  • IfA new gas line or branch is being addedThenYes. New piping is tested before it goes into service.
  • IfA section of pipe or a fitting is being replacedThenExpect a test of the repaired section, and ask whether the whole system will be tested.
  • IfOnly a flexible appliance connector is being swappedThenUsually the joints are leak-checked with solution or a detector rather than a full system test; ask the plumber.
  • IfA leak was reported but not yet foundThenPressure testing sections is one of the main ways to find it.

Passed versus failed

Test holds

  • Gauge stays steady for the full test period
  • Inspector can sign off where a permit applies
  • Walls, attic access or trenches can be closed
  • Gas is restored and appliances relit

Test drops

  • Gas stays off on that section
  • Joints are checked with detectors and leak solution
  • The leaking fitting or pipe is repaired
  • The test is repeated until it holds

Terms you may hear

Test gauge
A pressure gauge attached to the piping during the test, read at the start and end of the test period.
Rough-in test
A test done while piping is still exposed, before walls or trenches are closed.
Purging
Clearing air out of the lines when gas is reintroduced so burners light properly.
Isolation
Disconnecting or closing valves to appliances so they are not exposed to test pressure.

Questions to ask about the test

  1. What test pressure and duration will you use for this job?
  2. Will the appliances be isolated during the test?
  3. Will the inspector need to see the test, and who schedules that?
  4. Will you show me the gauge reading at the start and end?
  5. Who restores gas service and relights pilots afterward?

Common questions

How long does a gas pressure test take?

The required duration depends on the code and the system. Ask the plumber; the time is usually set by the inspector's requirements, not by convenience.

Can I be home during the test?

Yes. Gas is off on the section being tested, so plan around appliances such as the water heater or range being unavailable.

What if the test fails after a repair?

The plumber finds and fixes the leaking joint and repeats the test. Gas should not be restored to that section until it holds.

General information for Villa Park, not a quote or professional advice. In an emergency, call 911.