Bleed it once a year. Unless it’s steam.
If a radiator is warm at the bottom and cold at the top, it probably has air in it. On a hot-water system you can fix that yourself in five minutes.
First: steam or hot water?
Look at the radiator. A hot-water radiator has a small square or slotted bleed valve near the top on one end, and usually two pipes connected at the bottom. A steam radiator has a vent shaped like a little bullet or barrel sticking out of the side, and often just one pipe.
Steam radiators don’t get bled. Their vents let air out on their own. If a steam radiator is cold, the vent is usually clogged or the radiator is pitched the wrong way. That’s a call to us.
Bleeding a hot-water radiator
- Turn the heat up so the system is running and the pump is pushing water.
- Put a rag and a cup under the bleed valve.
- Turn the valve a quarter turn counterclockwise with a radiator key or a flat screwdriver. You’ll hear air hiss.
- When water comes out steadily instead of air, close it.
- Do the radiators farthest from the boiler and highest in the house first.
Then check the pressure
Bleeding lets a little water out. Look at the gauge on the boiler: most residential hot-water systems run at about 12 to 15 psi cold. If it’s dropped well below that, the system needs water added, and that’s the part to call us about if you’re not sure.
Still cold after bleeding? Call the shop.
The old-house plumber’s site, built in seven days.
Sixteen pages: house types drawn by hand, three generations of the family, an honest hourly rate explained, and a lead service line page written for Milwaukee.