It happens every year.
The heat's been running for a couple of weeks now and there's still one room, or one floor, that's cold.
So what's the problem? Is it major? Is it expensive? Do you need a plumber?
Well, the problem is fairly simple, and it may not be expensive, but you may need a plumber.
Before you call anyone, make sure the radiator valves (at the point where the pipes enter the radiator) are open, so water could be getting in. Then if there's still no heat, there are basically two things that could still be wrong.
*There may be air in a radiator that keeps the water from circulating. This is most likely the case if there's only one radiator that's not heating, or if there's a radiator that's only half hot.
If this seems to be the case, the radiator should be "bled" -- that is, the valve at the far end opened to allow air to escape. Most hardware stores have the "keys" that make this job simple. Turn the key slowly, no more than one turn, and put a cup under the valve -- you don't want a lot of water to come out, just a tiny bit
that indicates the air is gone.
*If more than one radiator is involved, or if bleeding doesn't help, there may not be enough water in the system, so the pressure is too low to keep water circulating to all the radiators.
"Lack of pressure shows up on the top floors first," says David Culver, of Bryan Plumbing and Heating in Parkville. He suggests examining the pressure gauge on the boiler. It's a small round or square device, usually on the top or front.
"The top section of the gauge is normally for pressure and the bottom section is for boiler temperature," Mr. Culver explains. Look for the pounds per square inch -- psi -- reading. "A pound of pressure will raise a column of water approximately 2.4 feet," Mr. Culver says.
What should the gauge say? He gives an example. "If a boiler has 10 pounds of pressure, it will raise the water 24 feet. In a typical two-story house with a basement, allow 8 feet for the basement, 8 feet for the first floor and approximately 4 feet on the second floor to get to the top of the highest radiator. Eight plus eight plus 4 is 20 feet, so 10 pounds of pressure would be plenty."
If you have higher ceilings, or no basement, adjust the figures accordingly.
If the psi reading on the pressure gauge seems too low for the height the water has to go, the system may need more water. Think of it as jamming more water into the system; that will raise the pressure.
And, if it's your first experience with a hot-water system, you may want to call in a plumber -- if for nothing else than to show you the ropes so you can proceed on your own next time.
Basically, here's what is involved in adjusting the pressure.
First the system should be cold, or at least not operating. Then determine whether the system has a pressure-reducing valve.
"The way to find it," Mr. Culver says, "is to follow the cold water line to the boiler. Just before it enters the boiler, there will be a shut-off valve, and right behind the shutoff valve is the pressure reducing valve." It's probably red or green, he says, and its purpose is to reduce the "street pressure" of the water as it enters the house from the usual 45 to 60 psi down to 12 pounds.
Most pressure-reducing valves, he explains, are preset at the factory to allow 12 psi, or to raise the water 28.8 feet. That's usually enough for a three-story house.
Some boilers have a "fast-fill" button on the valve that allows water to be added rapidly, at street pressure. Others have a set screw on the valve that should be turned clockwise to increase the pressure and counterclockwise to reduce it. Any adjustment has to be made gradually, to allow the system to adjust.
Some systems don't have a pressure-reducing valve; water is added by opening the valve in the main line from the street.
Generally boilers are protected by a pressure relief valve, factory set at 30 psi. If the pressure exceeds that, the valve will "blow" and the "excess" water will gush out. In some older houses, the pressure relief valve may run directly into a laundry tub or drain. (If you're rehabbing, be careful not to remove or cap such a pipe, Mr. Culver says.) In any case, you don't want to be standing next to the thing when it goes.
"Boiler pressure gauges are notoriously incorrect," Mr. Culver says. He recommends never raising the pressure above 25 psi.
Next: Different kinds of boilers.
Mr. Johnson is construction manager for Neighborhood Housing Services of Baltimore. Ms. Menzie is Home Editor of The Sun.
If you have questions, comments, tips or experiences to share about working on houses, write to us c/o HOME WORK, The Sun, 501 N. Calvert St., Baltimore, Md. 21278. Questions of general interest will be answered in the column; comments, tips and experiences will be reported in occasional columns.