How a gas pipeline leak test works, and why you should ask for it

A gas line you can see is easy to trust. The one behind the cabinets and through the wall is not, and the only way to know it is sound is to test it under pressure. This is what a proper test involves.

The pressure test

With the appliance disconnected and the line sealed at both ends, the installer pressurises it — with air or an inert gas, not with the fuel — to above working pressure, attaches a gauge, and waits. A sound line holds the reading. Any drop means a leak somewhere in the run.

How long

Long enough to see a slow leak, which means minutes, not seconds. A test that consists of pumping up and immediately declaring it fine has not tested anything.

The soap test

Once the line holds pressure, each joint, valve and connector is brushed with soap solution while pressurised. Bubbles mean a weep at that fitting. This finds the small leaks at threads and unions that a gauge might not resolve.

After connection

With gas on and the appliance connected, the joints are soaped again and each burner lit and watched. This is the check that the last metre — the connector and the appliance valve — is sound.

What you should be handed

• A test record with the pressure held and the duration
• The date and the installer's identification
• For a new PNG line, whatever certificate the supplier requires before opening the meter

Never test a gas line with a flame, and never let anyone else do so. If you suspect a leak on an existing line, close the valve, ventilate, and call. The test above is done on an isolated, unpressurised-with-gas line.

How often to repeat it

At installation, after any modification, and any time a joint has been disturbed — a new hob, a moved connector. It costs a little time and it is the difference between a pipe you assume is fine and one you know is.