A stove that sputters after months in a bin, or loses pressure halfway through a boil, is rarely a worn-out stove. It is a gummed jet, a dried seal, or fuel left sitting in the line, and all three turn up in the same short inspection run in the same order, before a single part gets swapped. Confirm the symptom, read the flame, then check the jet, the seals, the fuel line and its connections under soapy water, and how the stove was stored. A part is replaced only after a check has actually failed.
I run this on a concrete driveway, usually a Saturday morning in April, with the stove sitting on a folded shop rag so I can see what comes off it. The first thing I do is not open anything. I pump it up and light it.
The flame is the readout, and it points to which check to run first, so I watch it for a full minute before I touch a tool. A steady blue ring with that flat roar means the stove is fine and whatever I thought was wrong was probably my technique or the weather. A lazy yellow-tipped flame that won't take a full pump means too much fuel and not enough air, which usually means the jet. A flame that lights strong and sags means pressure is escaping somewhere behind the valve. A clean flame with fuel smell hanging in the air around the stove is the one I stop on, because a leak near a lit burner is not a tuning problem.
The jet, and the one tool that belongs in it
Fuel residue is what gums a jet and a generator tube, and it builds up quietly while the stove sits. Leftover fuel in the line oxidizes and leaves a varnish that narrows the opening. Nothing is worn. Something is coated.
The cleaning tool that shipped with your stove is sized for that orifice. On most liquid-fuel stoves it is a wire pricker clipped to the pump or a jet wrench with a needle in the handle, and it is designed to pass through the hole and scrape the wall without opening it. A sewing needle, a safety pin, or a bristle off a wire brush is not. Push one of those through and you have changed the orifice diameter, which sets the fuel flow. The stove then runs rich at every valve setting for the rest of its life. That is the one mistake in this whole routine that no amount of later cleaning undoes.
So the jet check comes down to two questions. Is the hole clear, and am I using the tool that was made for it? If your service instructions don't cover removing the jet, don't remove it. Work the pricker through the opening, or leave it alone and move to the next check.
Seals fail in the dark, which is why they hide
O-rings and pump cups dry, harden, and crack with age and fuel contact. They are the first thing I look at when a stove leaks or won't hold pressure, and they are the reason so many stoves get declared dead when they aren't.
On a liquid-fuel stove, look at the pump cup first. Leather cups need occasional oiling. A few drops of the oil your instructions specify, worked into the leather by hand and left to sit, brings a dry cup back. Soaked leather doesn't seal either, so go light. Synthetic cups don't come back. Once one stiffens or shows a crack, it's done, and it gets replaced with the cup specified for that stove, not with whatever fits.
Then the filler cap O-ring, the pump O-ring, and the small O-ring inside the valve. On a canister stove there are fewer seals and they matter more, because the one inside the valve where the canister threads on is doing most of the work. When it goes, you get a hiss at the joint and the smell of fuel, or a canister that frosts up faster than it should. Seals aren't a wear item you replace on a schedule. They're a check you run, and you replace the one that failed.
The fuel line is a storage problem wearing a parts costume
The generator tube on a liquid-fuel stove carries fuel past the burner, where heat vaporizes it before it burns. Residue coats the inside of that tube the same way it coats the jet, and the symptom is a stove that needs constant pumping, burns yellow, or won't hold a simmer no matter how you set the valve.
People read that as a tired stove. It's usually old fuel left in the line. Which makes this the check that isn't really a check, because the fix happens last fall. Store the stove clean and dry with fuel handled exactly the way the manufacturer's instructions say, and you limit the corrosion and varnish that form inside. Skip it, and every spring you're cleaning out a problem you created in October.
Soapy water first, match second
Before I put flame anywhere near a stove that might be leaking, I pressurize it with the valve closed and brush soapy water on the connections. A little dish soap in water, or kids' bubble mix, painted on with a cheap brush. Watch for bubbles that keep growing. A joint that holds is silent. A seal that's failing shows you exactly where it is, in daylight, with nothing lit and nothing hot.
That's the whole point. You're finding the leak before the leak finds you, at nine at night, at a trailhead, with cold hands and dinner still in the bag.
Light it on the driveway, not at camp
After everything is back together, I fill, pump, and light the stove outdoors on a hard surface, and I let it run longer than a single boil. Ten minutes at full output, then shut it down and let it cool, then lean in and smell for fuel. That test light is the last check before anything goes in the pack, and it catches most problems at home where a fix costs a rag and fifteen minutes instead of a meal.
What this routine won't do is resurrect a stove with a bent valve spindle, a cracked pump body, or a sealed assembly the manufacturer never intended anyone to open. Those go by the book, and if the book says don't touch it, I don't. It also won't explain a stove that misbehaves only in the cold or at altitude, because that's a fuel and pressure conversation, not a wear one. A technician reaches for a part as a conclusion, after a check has failed. Starting there is how a good stove ends up in the trash with nothing wrong with it.
