Air: The thing about air is that it's just about everywhere, which is good for people, but bad for steam systems. When you first start that steam system the pipes will be filled with air and air does a fine job of blocking the steam from getting to where you want it to go. And since you can't see air, you probably won't be thinking about it.

Steam and air are both gases, but they have different densities. Steam is lighter than air so the two won't mix. This is why the Dead Men invented the air vent. The air vent's job is to vent air. How about that! The vent belongs downstream of whatever it is you're trying to heat - be it a radiator, a kettle, a heat exchanger, an air-handling coil, or whatever. The steam has to be able to push the air through the heater and out of the system. The vent doesn't belong before the thing you're heating. It belongs after. Got it? Good!

When I'm troubleshooting steam, I always look for this first. Air will always be my Number One suspect. I walk the piping and ask myself this key question: "If I were air, could I get out?" And if I don't see a way out, neither will the air. If the air can't get out, the steam can't get in. It's as simple as that. The usual result is a cold heater. The usual reaction to this, unfortunately, is to raise the system pressure. Now, that's about the dumbest thing you can do because you can move more steam with a pinhole at the end of the pipe than you can with a ton of pressure back at the boiler. Try it once and you'll see what I mean. Vent the air from a point beyond the heater and most of your troubles will vanish. But try forcing the steam down a line that's filled with air and your troubles will multiply. The higher steam pressure will just compress the air. It will also hold condensate up in the system, increase the fuel bills, create water hammer, slam one-pipe steam air vents closed and never allow them to open again.

Think like air! Give it a way out because that's where it wants to go. And make sure the way out is downstream of whatever it is you're trying to heat. Get out of the boiler room. Take a walk around and keep your eyes open. If you were air could you get out?

Dirt: All steam systems are open to the atmosphere. They breathe air in and out. Steam condenses all over the place and wets the insides of the steel pipes. Put steel, air and water together and you'll get rust. That's where most of the dirt comes from. You have all these little flecks of rust that form on the insides of the pipes. The steam comes roaring along at a pretty good clip and rips those flecks off their perch. The condensate then carries the rust to the bottom of the system or the bottom of the heaters and there it stays, waiting to cause problems for you as time goes by.

Once it gets where it's going, the rust combines with whatever scale has dropped out of the water to form a sludge that looks like a primeval ooze left over from the birth of the Universe. If you get this stuff on your hands it's about as easy to remove as a tattoo. Needless to say, it will interfere with the operation of your system - clog up your air vents, return lines, calendar, mental process, etc.

Add to this evil slime the oil that's in the boiler when you first get it and life gets even more interesting. Boiler manufacturers have to thread the holes they cast in the iron. They use these BIG drills to do that. There's oil flowing all over the place and when that oil gets into the boiler you have to get rid of it if you're ever going to make decent steam. And this is why boiler manufacturers print cleaning instructions for all the boilers that they sell. If you read those instructions you'll learn how to clean the boiler and the system and avoid most of the problems that plague those who are in too much of a hurry.