After reconnecting an LPG (liquefied petroleum gas) bottle, it's common for a small amount of air to become trapped in the supply line. This air pocket can prevent your appliances from lighting or cause them to flame out shortly after ignition. The good news is that purging this air is usually a straightforward process a homeowner can do safely — but there are important limits to know before you start.
Why Air Gets Into the Line
When you disconnect an LPG bottle — to swap an empty one, for example — the gas pressure in the pipe drops to zero and air fills the void. When you reconnect and open the valve, gas pushes that air through the system. Until the air clears, your burners may click repeatedly without lighting, or light briefly then go out.
This is normal and not a fault with your appliances or regulator.
Safety First — Read This Before You Start
Gas work carries real risk. Before doing anything:
- Work outdoors or in a well-ventilated area. Never bleed gas lines in an enclosed space.
- No naked flames, cigarettes, or sparks anywhere nearby.
- Check for leaks first (see below) before attempting to light any appliance.
- If you smell gas strongly, or suspect a leak you cannot locate, do not proceed — ventilate the area, leave, and call a licensed gasfitter or your gas supplier immediately.
- Keep a fire extinguisher accessible when working around gas.
WorkSafe NZ has guidance on LPG safety that is worth reviewing.
What You Are Legally Allowed to Do
Under New Zealand law, gasfitting work is restricted and must be carried out by a licensed gasfitter registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). However, a homeowner is generally permitted to:
- Connect and disconnect an LPG cylinder to an existing, compliant regulator and pigtail (the flexible hose fitting).
- Operate appliance controls (knobs, igniters) to purge air from the line.
You are not permitted to modify pipework, replace regulators, or alter any gas fittings — that is restricted gasfitting work.
Step-by-Step: Bleeding Air From an LPG Line
1. Reconnect the Bottle Correctly
- Ensure the bottle valve is fully closed before connecting.
- Thread the regulator coupling onto the bottle valve. LPG fittings in NZ use a left-hand (reverse) thread — turn the nut anti-clockwise to tighten.
- Hand-tighten firmly, then snug up with a spanner. Do not over-torque.
2. Check for Leaks Before Opening the Valve
- Mix a small amount of dish soap with water and brush it onto all connections — the bottle valve, the regulator coupling, and any accessible joints.
- Slowly open the bottle valve one full turn.
- Watch for bubbles. If you see any, close the valve immediately, re-tighten the fitting, and recheck. If bubbles persist, do not proceed — call a licensed gasfitter.
- No bubbles means you have a gas-tight connection.
3. Purge the Air at an Appliance
- Open the bottle valve fully.
- Go to the appliance furthest from the bottle (e.g., a cooktop burner).
- Turn the burner knob to the ignite/light position and hold it in while pressing the igniter, or use a long lighter.
- The burner may click many times or briefly flicker before lighting — this is the air clearing. Keep attempting ignition for up to 30–60 seconds.
- Once the burner lights, let it run for 10–15 seconds, then turn it off.
- Repeat at other appliances if needed — usually one burner is enough to clear the line.
4. If the Appliance Still Won't Light
- Check the bottle is not empty — weigh it or check the gauge if fitted.
- Confirm the regulator is the correct type and pressure rating for your appliances (most NZ domestic LPG systems use a 2.75 kPa regulator).
- If the appliance still fails to light after several attempts, there may be a fault with the regulator, pigtail, or appliance itself. Stop and call a professional.
Bottle Changeover Tips
| Situation | Action |
|---|---|
| Bottle feels very light / gauge reads empty | Replace bottle before bleeding |
| Strong gas smell after opening valve | Close valve, ventilate, call gasfitter |
| Regulator or pigtail looks cracked or aged | Do not use — have a gasfitter replace it |
| Appliance lights but flame is yellow/orange | Possible air-gas mix issue — call gasfitter |
Regulators and pigtails have a service life — check with your gas supplier or a licensed gasfitter if yours looks worn. MBIE Building Performance sets out the NZ Building Code requirements (including G12 for gas installations) that all gas work must comply with.
When to Call a Professional
Call a licensed gasfitter (find one via the PGDB register or on tradedirectory.co.nz) if:
- You can smell gas and cannot identify the source.
- Soap-bubble testing reveals a leak you cannot fix by re-tightening.
- Appliances still won't light after purging.
- The regulator, pigtail, or any pipework looks damaged, corroded, or has been modified.
- You are unsure about any step in this process.
A qualified gasfitter can also carry out a full pressure test of your system to confirm there are no hidden leaks — a worthwhile check if the system has been unused for a long time.