Thump, thump, thump. Probably what you heard over Halloween wasn't spooks or poltergeists at all. If your heat was on, those strange noises more likely came from your radiators.

Fact: Air in the radiators can cause them to make strange noises.

Fact: Air in the radiators can cause them to heat less.

Fact: Enough facts. On with the story.

Many homes have a boiler that heats the water that circulates throught the radiators that heat the house. Water, however, contains tiny bubbles of air. Tiny bubbles can become big bubbles, if they have a mind to. Big bubbles -- remember Three-Mile Island? -- are not funny. They can block the flow of water, causing a perfectly healthy looking radiator to go limp and cold.

You must get it out.

After a few thousand years of making radiators, manufacturers noticed that sometimes their radiators became clogged with air. That was when they decided to put a little valve on the end of the radiator to let the air out.

If you suspect you have air in the system, first turn the heat off. Then, if you have baseboard radiators, remove the cover and locate the valve.

Some valves open with a screwdriver. Others require a key. Maybe you lost the key. You can buy a another at a hardward store.

Place a cup, a dish, a can a bowl -- whatever -- under the valve to catch any water that comes out. Then open the valve. If you hear a hissing noise, then you know for sure you don't have poltergeists. That's air. Wait until the hissing stops and water starts to stream out.

Do not leave the room while the valve is open.

When water starts to come out, close the valve.

In some circles it is said that each year before the heating season begins the entire system, from the boiler up, should be drained and cleaned out. But a recognized authority in the area, James Healy, the director of education with the zed authority in the area, James Healy, the director of education Northamerican Heating and Air-conditioning Wholesalers Association in Columbus, Ohio, says this is nonsense.

After you drain the system, you have to fill it up again and "any time you introduce new water," Healy said, "you're adding contaminants. You're adding air and increasing the likelihood of rust and corrosion. You've got scads of places that can introduce leaks. The tighter the system the better." s

If you bleed the radiators and they still are not heating, then the problem may lie elsewhere, such as in the expansion tank.

The expansion tank is located near the boiler. The reason it's there is to catch any overflow from the rest of the system (water expands when heated) so that if one of the radiators is blocked, it doesn't take off like a rocket through the upstairs bedroom and into your neighbor's yard.

The expansion tank usually contains a balance of air and water. The newer systems have a diaphram that separates the two. Some older expansion tanks, however, can become waterlogged.

You will know the tank is probably waterlogged if the needle on the pressure guage is jumping amorously toward the red zone. Normally the guage should read somewhere between 8 to 12 pounds for a two-story house, around 4 pounds for a one-story house.

If you are not handy around the house, you may not want to fiddle with the expansion tank. If you know your system well enough (if you know what all the little valves and pipes are for), you may be equipped to drain the tank yourself.

This done and still no heat, either you forgot to turn on the boiler in the first place or you have real problems and should definitely call your heating man.

If you steam heat, it's recommended that before you turn the boiler on you remove the safety valves on the radiators and clean them out in a solution of trisodium phosphate (available in hardware stores).

Also vacuum the radiators. Dust can prevent them from heating efficiently.

Remove the cover from the thermostat and blow out any dust thay may have collected there.

Now you're ready to forget the whole thing and buy a wood stove.