What is proper operation of radiator vents?

Big Al

Thanks. At least something's normal in my house!

J

Janet_4

Please excuse my ignorance. This is my first year in a house with steam heat. Each radiator has a silver air vent thing on it. A few minutes after the boiler starts up they start to quietly let out air. After a while they all close one by one. I assume that means that steam has reached them. However . . . after a few minutes they start opening up individually again for a couple of seconds . . . and then close again (a little louder now.) The smallest radiator might do this once or twice, but the huge radiator in the living room might do this several times a few minutes apart. It makes a sound like ssssssshhht . . . kind of like air, then wet steam, then shut. btw: The gage on the boiler never seems to go above 2.

Once steam reaches the end of the radiator, shouldn't the vent stay shut? Or does it take a few tries to get all the air worked out of a big radiator? Is it normal for the vents to re-open sometimes? Or is this a problem? Do I need to call in a service tech?

Thank you,

J

Steamhead (in transit)

This is normal

the vents close on temperature. When they close, no more steam can get in, so they cool down, re-open, heat up again and close.

The time when this should happen most is when you've turned up the heat in the morning and the boiler runs for a while.

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Janet_4

This is such a great site!

I was reading about steam problems here and the article said that hissing radiator vents are abnormal. Well, when my boiler is warming up, my vents are pretty quiet until they all close the first time, but when they open again later, they do hiss a lot louder, even if the gage on the boiler is barely above zero. It looks like the boiler pressure is turned down as far as it can go and the gage never even gets to 2.

How can radiator vents be quiet all the time if they are letting pressure out?

J

Steamhead (in transit)

This may be

a plugged Pressuretrol pigtail, allowing the pressure to rise more than it should. Have a pro check it as this is a safety issue. If it's plugged, and it's made of steel, it should be replaced with a brass one since these are less prone to plugging and are easier to clean.

Try the Find a Professional page of this site, under Resources above.

"Steamhead"

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Janet_4

I think you mean that loop of metal tube that the pressure control is on. The boiler was just serviced before we moved into the house in September. He took apart some pipes and flushed out lots of dark water from the inside of the boiler and took off the box with the pressure switch (it has a tube of mercury in it) and cleaned out that pigtail. I think he called it a siphon tube. The gage was replaced too, and it is on a separate pipe from the pigtail. The switch is set at less than 2 and, the boiler shuts off when the gage gets to about 1 and 1/2. I think that's working OK.

The vents that hiss the loudest were just replaced. They are salt shaker sized cylinders with a thimble sized one on top. There are silver "hats" on them. You can loosen a screw and twist the hat to cover up the hole. The old ones look like pointy silver bullets and are much quieter. The hole in them looks much smaller than the new ones. The new ones also make a loud pop when they open and close.

Could the new vents be bad ones?

Thanks,

J