Inspecting the Propane System Safely

The propane (LP) system is the one part of a used RV that can hurt you, so treat it with respect and verify it before you hand over money. The good news: most propane problems are cheap to fix (a new regulator runs roughly $40 to $90, a fresh tank certification is $25 to $60), but the dangerous ones (leaks at fittings, a corroded regulator, a soft hose) are exactly what a seller is hoping you skip. Do a calm, methodical check, insist on a working leak test before the deal closes, and never light anything you have not confirmed is tight.

Propane is heavier than air. That single fact explains almost every safety rule below. If it leaks, it does not rise and vent like natural gas in a house. It pools low (in the belly, the storage bay, the floor) and waits for a spark. So your job as a used-RV buyer is not to become a certified LP tech. Your job is to find the obvious problems, confirm the system holds pressure, and price the rest into your offer. When you are ready, paste the listing and get your RV verdict so the propane notes land next to the rest of the unit's story.

First Rule: How to Stay Safe During the Inspection

Before you touch a single valve, set the ground rules. These are not optional.

• No flames, no smoking, no vaping anywhere near the RV during the propane check. Not yours, not the seller's.
• Nose first. Propane is odorless, so manufacturers add a rotten-egg / skunk smell (ethyl mercaptan). If you smell that strongly the moment you open a bay, stop. Do not operate switches, do not flip the fridge to gas, walk away from the unit and ventilate it before going further.
• Open it up. Do the inspection with windows, the door, and storage bays open. You want any small release to dissipate, not collect.
• Hands off the appliances until the bottles are confirmed tight. You test the system for leaks first, then you light burners, never the other way around.
• Watch the seller's body language. A seller who gets twitchy when you say "let's do a proper leak test" is telling you something.

If at any point you are not comfortable, that is a normal and smart place to be. A mobile RV tech doing an LP-specific inspection typically charges $90 to $175, and a full pre-purchase inspection runs $150 to $400 depending on region and rig size. On a $20,000-plus purchase, that is cheap insurance. Verify pricing locally, it varies.

The Two Pieces That Age Out: Tanks and the Regulator

Two propane components have real expiration logic, and both are common negotiation points on a used rig.

Tanks and cylinders. Travel trailers and most towables use removable DOT cylinders (the upright bottles, usually 20 lb / 5 gallon or 30 lb / 7.5 gallon). Motorhomes usually have a permanently mounted ASME tank. The difference matters at refill time:

• DOT cylinders must be re-certified 12 years from the manufacture date stamped on the collar, then every 5 years after. An expired bottle is not illegal to own, but many refill stations will refuse to fill it. Re-certification is roughly $25 to $60, or you simply buy a new cylinder ($45 to $120 for a 20 or 30 lb bottle, verify current pricing).
• ASME tanks (motorhomes) do not carry the same recurring re-cert requirement, which is a quiet plus when you shop a Class A motorhome or Class C motorhome.

Check the date stamp. On a travel trailer or fifth wheel, pop the cover and read the collar. If both bottles are 11-plus years old, that is a small, predictable cost, not a deal-killer, but it is a fair $50 to $150 ask off the price.

The regulator. This is the small (often two-stage) device between the bottles and the rig that drops tank pressure down to the appliance level. Regulators wear out. The rule of thumb most techs use is replace it around every 10 to 15 years, sooner if you see corrosion, rust streaks, or a clogged/missing vent.

All ranges are typical. Verify on the specific unit, because age, climate, and storage change everything.

The Walk-Around: What Your Eyes and Nose Find First

You can catch most of the obvious problems without a single tool. Work bottles to appliances.

At the bottles and regulator:

• Rust or white powdery corrosion on the regulator body. A corroded regulator is a replace item, not a clean item.
• The regulator vent should point down and be clear (not packed with mud, a wasp nest, or paint). A blocked vent makes a regulator misbehave.
• The rubber pigtail hoses: flex them gently. Cracked, sun-baked, sticky, or rock-hard rubber means replacement. These are cheap ($15 to $40 each) but a tell about how the rig was stored.
• The changeover indicator (on dual-bottle setups) should show green when there is gas and flip to red when a bottle runs empty.

Along the lines:

• Copper or black-iron lines running under the rig should be secured, not dangling or rubbed shiny where they cross a frame member. A chafed line is a future leak.
• Green/blue crusty deposits at any fitting can signal a slow leak that has been weeping for a while.

At the appliances:

• The water heater burner area and the furnace exterior vent should be free of soot. Black soot streaks above a vent suggest incomplete combustion (a dirty or misadjusted burner).
• The fridge burner area (accessible from the outside lower vent) should not be packed with rust flakes, mud-dauber nests, or spiderwebs, which are a classic cause of a propane fridge that will not stay lit.

If the propane reveals general neglect, that often rhymes with other deferred maintenance. Pair this with your broader walk and the used RV inspection checklist, and keep an eye on the RV red flags list.

The Leak Test: Do Not Skip This

This is the heart of a propane inspection, and it is the step sellers most often "forget" to offer. There are two practical ways to verify the system holds pressure.

Option 1: The built-in manometer / timed pressure test (best). Many RVs have a low-pressure test port, and most mobile techs carry a manometer. The test pressurizes the system, then watches whether pressure holds for a set time (commonly a few minutes) with all appliances off. If pressure drops, there is a leak somewhere. This is the gold standard, and it is exactly what your $90 to $175 LP inspection buys you.

Option 2: The soap-bubble check (you can do this). With the bottles on and appliances off, brush a soapy water solution (or a purpose-made leak-detector spray) onto every fitting: the bottle connections, the regulator inlet and outlet, the pigtails, and any accessible joints. Growing bubbles = escaping gas. This will not catch a tiny pinhole the way a manometer will, but it reliably finds the leaks that matter at connections. Never, ever use a flame to check for leaks. People still do it. People still get hurt.

Walk-away or renegotiate if:

• The seller refuses a leak test or "the gauge is broken, trust me."
• You can smell propane and cannot quickly trace and stop it.
• A fitting bubbles and the seller waves it off as "it always does that."
• The regulator is visibly corroded and the seller insists it is fine.

A failed leak test is not automatically a walk-away. Often it is a $20 fitting or a $40 to $90 regulator. But it absolutely changes your offer and your timeline, and it should be fixed before you tow or drive the rig home.

Test Every Gas Appliance, One at a Time

After the system is confirmed tight, light things up. Do each appliance individually so you know exactly what works.

1. Stovetop burners. Each should light quickly and burn a steady blue flame. A lazy yellow or orange flame, lots of flicker, or a burner that takes many clicks suggests a gas-delivery or air-mixture issue (sometimes just spiders in the orifice, sometimes the regulator).
2. Oven. Lights and holds. Many used-RV ovens are crusty from disuse, which is cosmetic, but confirm it actually fires.
3. Furnace. Set the thermostat above room temp. You should hear the blower, then the burner ignite, then warm air. A furnace that clicks and clicks without lighting (no whoosh) is a no-light fault. Furnace repairs range widely, a sail-switch or board issue can be $150 to $500-plus, verify by symptom.
4. Water heater. If it runs on gas (many are gas/electric), switch to gas, listen for ignition, and confirm it heats. A water heater that lights then drops out can be a thermocouple or a sooted burner.
5. Absorption fridge (gas mode). This is the slow one. On propane, an absorption fridge can take several hours to get cold, so you may not get a full verdict at the curb. At minimum confirm it ignites on gas and the flame is present (you can often see the glow through the lower outside vent). A fridge that will not light on gas but works on electric is one of the most common, and most annoying, used-RV propane complaints.

If a propane appliance only works on electric, treat the gas side as unverified, not as working. That distinction is worth real money at the table.

Tie it into the bigger electrical and safety picture

The propane system overlaps with the rig's safety electronics. Confirm the LP/propane leak detector (a small panel near the floor, since propane sinks) powers on and is not past its replacement date (these expire, typically 5 to 7 years, and a chirping or dead unit is a $30 to $60 fix). While you are in there, sanity-check the carbon monoxide alarm. For the wider system, see RV electrical problems, and if the rig has a generator, fold in generator hours.

Questions to Ask the Seller

How a seller answers tells you almost as much as the hardware does.

• "When was the regulator last replaced?" (Vague answer = assume it is original.)
• "Have both bottles been re-certified, and what is the date stamp?"
• "When did you last run the furnace, water heater, and fridge on propane?"
• "Has the system ever been leak-tested, and do you have a record?"
• "Has any LP work been done by a shop, and do you have the invoice?"
• "Where do you fill the bottles, and have you ever been refused a fill?" (A refused fill points straight at an expired cylinder.)
• "Has the propane leak detector ever gone off?"

Documented LP service is a green flag. "It all works, I just never use it" on a 12-year-old rig is a yellow flag, because never-used absorption fridges and furnaces are exactly the ones that fail when you finally light them.

What This Should Cost You to Make Right

Use this to price your offer with the used RV offer calculator. Most propane fixes are minor, which is good news for a nervous buyer: this system rarely sinks a deal by itself, unlike water damage signs or soft floor.

Ranges are typical and regional, verify on the specific unit. The big swing is the absorption fridge: a clean-and-relight is cheap, but a failed cooling unit can run four figures, so confirm gas-mode cooling before you assume the fridge "works."

Frequently Asked Questions

Is it safe to buy an RV with an old propane system? Usually yes, as long as you leak-test it and budget for the aging parts (regulator, hoses, cylinder re-cert). Propane systems are simple and serviceable. The danger is not age itself, it is an untested system, a corroded regulator, or a leak nobody checked. Confirm it holds pressure and you have removed most of the risk.

Can I just smell for a propane leak? Smell is your early warning, not your inspection. The added odorant is strong, so a big leak is hard to miss, but slow weeps at a fitting may not register by nose. That is why the soap-bubble check and a proper manometer test exist. Trust your nose to start, prove it with bubbles or a gauge.

Do propane tanks really expire? DOT cylinders (the removable bottles on towables) need re-certification at 12 years, then every 5 years. They do not "expire" as garbage, but many stations will refuse to fill an out-of-date bottle. ASME tanks on motorhomes do not carry the same recurring requirement. Always read the date stamp on the collar.

Should I tow or drive an RV home with the propane on? General guidance is to travel with bottles off unless you specifically need the fridge running on gas, and many areas require propane off through tunnels and at fueling stations. For a unit you just bought and have not fully leak-tested, keep it off in transit and verify the system properly once you are home.

Who should actually inspect the propane system, me or a pro? You can and should do the visual, smell, and soap-bubble checks yourself, plus light every appliance. For the timed pressure test and anything that smells off, bring a mobile RV tech ($90 to $175 for an LP-focused visit). On a four or five-figure purchase, that is a small, smart spend.

Found a used RV you are serious about? Paste the listing and get your RV verdict.