Purging air from a new LPG bottle connection is an important safety step — air mixed with LPG in your pipework can prevent appliances from lighting properly and, in some situations, create a hazard. For a simple bottle swap on an existing, compliant system, there is a straightforward process a homeowner can follow. However, if you are connecting new pipework, installing a regulator, or working on anything beyond a standard bottle changeover, this becomes restricted gasfitting work that must be carried out by a licensed professional.
Why Purging Matters
When you connect a new LPG cylinder, air is present in the hose and regulator. If that air reaches your appliance burner, it can cause ignition failure, delayed ignition (a small "pop"), or an incomplete burn. Purging simply means allowing a small, controlled amount of gas to displace that air before you attempt to light any appliance. Done correctly and in a well-ventilated area, it is a quick and safe process.
What Homeowners Can Legally Do
Under New Zealand law, gasfitting work is restricted work regulated by the Plumbers Gasfitters & Drainlayers Board (PGDB). However, a homeowner is generally permitted to connect and disconnect a standard LPG cylinder (bottle) to an existing, compliant appliance or system — for example, swapping a 9 kg BBQ bottle or a 45 kg home-heating cylinder on an already-installed regulator and hose assembly.
You must not attempt to:
- Install, alter, or repair gas pipework or fittings
- Replace or adjust a regulator (other than a simple POL-to-appliance swap on a portable appliance, and even then, check with your supplier)
- Connect gas to any new installation
If in doubt, contact the PGDB or a licensed gasfitter to confirm what you are allowed to do.
Step-by-Step: Purging a New LPG Bottle on an Existing System
Before you begin, make sure you are working outdoors or in a very well-ventilated area, away from any ignition sources (open flames, cigarettes, electrical switches).
What you will need
- The new LPG cylinder
- A correctly rated POL spanner or hand-tight POL fitting (depending on your regulator)
- Leak-detection spray or soapy water
- A cloth
The process
- Turn off all appliances connected to the gas system before you start.
- Close the cylinder valve on the new bottle before connecting.
- Connect the regulator to the new cylinder. LPG POL fittings are left-hand thread — turn anti-clockwise to tighten. Hand-tight is usually sufficient for POL connections; do not over-torque.
- Check for leaks first. Open the cylinder valve slowly (one full turn) and apply leak-detection spray or soapy water to the connection point. If you see bubbles, close the valve immediately, disconnect, and inspect the fitting and O-ring. Do not proceed until the connection is leak-free.
- Purge the air. With all appliance valves and burner controls still off, open the cylinder valve fully. Wait approximately 30–60 seconds. This allows gas pressure to push air through the regulator and hose toward the appliances without releasing gas into the room (since appliance valves are closed).
- Light the nearest appliance following the manufacturer's instructions. The first ignition attempt may take a couple of tries as the last of the air clears. This is normal.
- Once the appliance lights and burns steadily with a stable blue flame, the system is purged and ready to use.
Safety note: Never purge gas into an enclosed space. Never use a naked flame to check for leaks. If you smell gas strongly at any point, close the cylinder valve, move away from the area, ventilate the space, and call your gas supplier or a licensed gasfitter.
Checking Your Regulator and Hose
While you have the bottle disconnected, it is a good time to inspect your regulator and hose for signs of wear, cracking, or damage. LPG hoses and regulators have a recommended service life — check the date stamp on your hose and refer to your appliance or regulator manufacturer's guidance. Replacing these components is restricted gasfitting work and must be done by a licensed gasfitter.
For compliance requirements, the MBIE Building Performance website outlines how the NZ Building Code (including clauses relating to gas installations) applies to residential properties.
When to Call a Professional
Call a licensed gasfitter if you are:
- Installing a new gas appliance or connecting gas for the first time
- Replacing or relocating pipework, regulators, or fittings
- Experiencing repeated ignition failures even after purging
- Unsure whether your existing installation is compliant
- Dealing with a suspected gas leak that does not resolve after closing the cylinder valve
A licensed gasfitter will also issue you a Certificate of Compliance (CoC) for any restricted work, which is important for insurance and resale purposes. You can find qualified local gasfitters on tradedirectory.co.nz.
For rental properties, landlords should also be aware of Healthy Homes standards and ensure all gas appliances are safely installed and maintained.
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