How to Change a Gas Bottle on Your Hot Water System

If your gas hot water suddenly runs cold, the most common cause is an empty LPG cylinder. The short answer: turn the empty bottle off, turn the full bottle on, flip the changeover lever towards the full bottle, check for leaks with soapy water, then relight or reset the water heater. Do not disconnect or reconnect 45 kg cylinders yourself — book your gas supplier or a licensed gasfitter to do the swap.

What you can do yourself (and what to leave to the pros)

Most Aussie homes on bottled gas use two 45 kg cylinders outside with a regulator and a changeover lever. As a householder you can safely:

• Turn cylinder valves on/off.
• Operate the manual/automatic changeover lever.
• Relight or reset the hot water unit following the manufacturer’s instructions.
• Do a simple soapy-water leak check on exposed joints after you switch over.

You should not attempt to disconnect or reconnect 45 kg cylinders, replace pigtails/regulators, or move cylinders. Those jobs require a licensed gasfitter and, for cylinder swaps, are usually done by your LPG supplier at delivery. If you’re unsure what’s allowed in your state, check with your supplier or your state gas regulator.

Know your setup: twin bottles and changeover regulators

Look at the cylinders and the regulator mounted between them:

• Two cylinders (45 kg typical): One is “in service” and the other is the standby.
• Regulator with a lever or knob: This selects which cylinder is feeding the house. Some regulators are automatic (they switch over internally when one bottle empties) and show a red/green indicator. You still need to turn the full bottle on and reset the lever after an automatic changeover.
• Shut-off valves on top of each bottle: Turn clockwise to close, anti-clockwise to open (hand-tight only).

Many setups have a small window or pointer that goes red when the “in service” bottle runs out. That’s your cue to open the full bottle, flip the lever, and book a refill/exchange for the empty.

Step-by-step: how to change gas bottle for hot water (switch to the full cylinder)

Before you start:

• Do it outdoors in daylight if possible. Use a torch at night — never a flame.
• Keep flames, cigarettes and ignition sources well away.
• If you smell strong gas near the cylinders or hear hissing you can’t locate, turn both bottles off, keep clear and call your supplier or a licensed gasfitter.

1. Turn the empty bottle off. Rotate its handwheel fully clockwise.
2. Open the full bottle. Turn its handwheel anti-clockwise all the way, then back a quarter-turn so it’s not jammed fully open.
3. Flip the changeover lever. Move the lever so it points to (or selects) the full bottle. On some automatic regulators, this “resets” the indicator from red back to green.
4. Leak-check with soapy water. Mix dishwashing liquid and water in a spray bottle. Spray the visible joints at the cylinder outlet and regulator. Look for growing bubbles. If you see any, turn the bottle off and call your supplier or a licensed gasfitter. Do not use a flame.
5. Relight or reset the hot water unit. See the next section for common procedures.
6. Book a refill/exchange for the empty cylinder. Your supplier will deliver, connect and leak-test the replacement 45 kg bottle.

Relighting or resetting your gas hot water unit

Continuous flow (instant) units

• Power and isolation: Ensure the unit has power (240 V or batteries, if used) and the external gas isolation valve beside the unit is ON (inline with the pipe).
• Reset: Turn the power off and back on at the unit’s switch or powerpoint. Open a hot tap for 20–30 seconds to purge air and allow ignition.
• Temperature: Confirm the controller is set to your usual temperature (often 50–60 °C).

Gas storage hot water

• Pilot ignition models: Follow the lighting instructions on the front panel exactly. Typically: turn gas control to OFF and wait 5 minutes; turn to PILOT; hold down the pilot button while pressing the igniter until you see the pilot flame; keep holding for 30–60 seconds; turn to ON.
• Electronic ignition models: Restore power, ensure gas is on, and cycle the thermostat or power to trigger ignition.

After relighting, it can take a few minutes for continuous flow units to stabilise, and for storage tanks it may take 30–60 minutes to recover hot water if the tank cooled.

Safety checks after you switch bottles

• Smell check: A faint gas whiff right after opening a valve can be normal. Persistent gas smell is not — turn off the bottle and call a pro.
• Frosting/ice: A little frost on the cylinder during heavy draw isn’t unusual. Heavy icing or regulator icing that stops gas flow points to a supply/regulator issue. Switch to the other bottle (if available) and call your supplier.
• Cylinder position: Cylinders must be upright, on a firm base, secured, and in a well-ventilated outdoor spot. Don’t enclose them or store items against them. If clearances look non-compliant, ask your supplier to review.

If it still won’t work: quick troubleshooting checklist

Work from most likely to least:

1. Is the “full” bottle actually on? Open the handwheel fully, then back a quarter-turn. Confirm the lever is pointing to that bottle.
2. Air in the line. Open a hot tap for 30–60 seconds to purge air and allow the unit to ignite.
3. Appliance reset needed. Power-cycle the continuous flow unit; for storage units, re-light the pilot per the label.
4. External isolation valve off. Check the small lever valve beside the hot water unit is in line with the pipe.
5. Low gas supply or regulator fault. If both bottles are open and selected but the unit won’t stay lit, the regulator or pigtail may be faulty. Turn bottles off and call a licensed gasfitter.
6. Weather/wind effects. Strong wind can blow out pilots or affect flues. Shield temporarily and relight; if it recurs, have a gasfitter check the flue/venting.
7. Appliance fault code. Many continuous flow units show a code. Note it and contact a service technician.

Ordering a replacement cylinder

As soon as you’ve switched to the full bottle, arrange a refill/exchange for the empty one. Your LPG supplier will deliver the 45 kg cylinder, move it into place, connect it to the regulator, and leak-test. If your site is tricky (tight access, steps, soft ground), mention it when booking to avoid delays.

If you regularly run out of gas, ask your supplier about an automatic changeover regulator (if you don’t already have one) and consider adding a delivery schedule. Also consider whether your hot water demand has grown — a service tech can check appliance efficiency and advise on cylinder capacity and placement.

Common questions and good habits

• How long will a 45 kg bottle last? It varies with household size and water use. Many families get a month or more from one bottle when only hot water is on LPG. Track your usage for a season and set a reminder to check the indicator weekly.
• How to tell which bottle is empty? The changeover indicator may show red; the empty bottle often feels lighter and may show a frost line when it ran out. The safest check is to open the suspected full bottle, select it with the lever, and see if hot water returns.
• Leak checks: Keep a small spray bottle of soapy water near the cylinders. After any switch or delivery, a quick spray on visible joints helps catch issues early.
• Keep clearance and access: Don’t stack firewood, bins or garden gear around cylinders. Clear, ventilated access helps your supplier and keeps you compliant with Australian Standards.

Switching your hot water across to a full LPG bottle is simple and safe when you follow the steps above. Leave cylinder swaps and any repairs to the pros, and you’ll stay warm, compliant and hassle-free.