LPG runs your cooktop, hot water, sometimes your fridge and (on some models) your heater. The system is simple in principle — bottle → regulator → pipework → appliance — but it has rules. Here's how it works, and where the safety lines are.
The Three Main Parts
1. Gas Bottles (Cylinders)
Mars caravans typically run two LPG bottles in a vented gas locker. Common sizes:
- 4kg — small, lightweight, fewer cooking hours.
- 9kg — the most common caravan size.
- 4.5kg — occasional alternative.
Bottles have a test date stamped into the collar. They must be re-tested every 10 years. Out-of-test bottles can't legally be refilled or swapped.
2. The Regulator
Sits at the top of the gas locker and reduces the high-pressure gas from the bottle to the low (2.75 kPa) pressure your appliances run on. Most Mars vans have a changeover regulator that lets both bottles connect at once — one runs, the other waits. When the first empties, you switch the lever; the second takes over without losing supply.
Regulators have a typical service life of 10 years and should be replaced at gas certification (more on that below).
3. Pipework & Lines
- Pigtails — flexible hoses connecting each bottle to the regulator. These wear out faster than the regulator and typically need replacing every 5 years.
- Copper or stainless lines — run from the regulator through the van to each appliance.
- Isolation valves — usually one before each appliance. Use these for service work; never use them as a substitute for turning the bottle off when travelling.
What Gas Runs in Your Van
Standard appliances that typically run on gas in Mars vans:
- Cooktop (and grill, if fitted)
- Hot water system (gas-only or gas+electric)
- Some heaters (Truma Combi systems, dual-fuel heaters)
Newer Mars models often use induction cooktops and diesel heaters, reducing gas reliance. Check what your specific build runs on.
The Travel Rule You Must Know
Both gas bottles must be turned off at the bottle (not just at the regulator) when towing.
Why: in the unlikely event of a collision or fitting failure, you don't want pressurised gas escaping. This is also a legal requirement when crossing certain bridges, tunnels and ferries — and on most car ferries (Spirit of Tasmania included).
See Why You Must Turn Off Your Gas Bottles When Travelling in the existing help centre.
How Long Does a Bottle Last?
Rough estimates for typical use:
- Cooktop alone (2 burners, 30 min/day): a 9kg bottle ≈ 3–4 weeks
- Cooktop + gas hot water (daily showers): a 9kg bottle ≈ 10–14 days
- Cooktop + hot water + heater on cold nights: a 9kg bottle ≈ 5–7 days
Two 9kg bottles, used efficiently, comfortably get most couples through a week to two weeks of full-use off-grid.
Where to Refill or Swap
- Refill — your bottle goes onto a gas refill station's scale and is topped up. Usually cheaper per kg. Available at many service stations, Bunnings, ag/rural supply stores, BBQ shops.
- Swap-and-go — exchange your empty for a full one. Convenient (especially after-hours at service stations) but pricier per kg, and you don't choose the bottle you get back.
For long trips, refill where you can — cheaper and you keep your own bottles.
Annual Gas Certification
Most states require periodic gas certification on caravans (and on rental/hire vans specifically). The certificate confirms the system is safe and the components are within their service life. See Annual Gas Certification: What's Legally Requiredfor the detail by state.
What's an Owner Job vs a Gas Fitter Job
You Can Do
- Swap a gas bottle
- Switch the changeover regulator lever
- Turn isolation valves on/off
- Use a soapy water leak test on bottle-to-regulator connections (see article on swapping a bottle)
Licensed Gas Fitter Only
- Any work on the regulator or copper lines
- Any appliance installation, removal or repair involving gas connections
- Pressure testing
- Issuing the gas safety certificate
- Adding new gas points or relocating existing ones
DIY work on the gas system isn't just dangerous — it's illegal, and it voids your warranty and insurance.
Warning Signs of a Gas Problem
- Smell of gas anywhere — even faintly
- Appliance flame is yellow instead of blue (incomplete combustion)
- Gas bottle gauge dropping unexpectedly fast
- Hissing near any fitting
- Soot deposits around an appliance
- CO alarm sounding
If you smell gas — see "I Can Smell Gas" — What to Do Right Now. Don't wait.
Smart Habits
- Turn bottles off when not in use, even at camp — extra layer of safety.
- Keep the gas locker vents clear — they're there for a reason.
- Don't store anything else in the gas locker. Just bottles.
- Carry a small bottle of dish soap for the soapy-water leak test (cheaper than commercial leak detectors and works as well).
- Get the system certified on schedule — usually annually or every two years depending on state and use.
Related: How to Safely Swap a Gas Bottle· "I Can Smell Gas"— What to Do Right Now