Is this normal?

betty_2

Gentlemen,
I fired up my heating system today to test everything prior to cold weather. The boiler heated up fine. The radiators began to heat the air vents closed. As the boiler continued to run, the air vents on the radiators OPENED again to emit air.
Is this Normal?

Thanks

Brad White_200

Yes

If the bellows in the radiator falls below steam temperature, it will open.

If the boiler is "in retreat" (shut down on reaching pressure between cycles), the vacuum will draw air in.

If there is still steam produced at the boiler and the vent happens to be open (because the steam has not filled that particular radiator), then the open vent will release what air is ahead of it. Once steam hits the vent bellows, the vent will close.


Wonderful that you are paying attention to the details, Betty.

betty_2

Your 2nd to last line Brad didn't make sense to me.
If their is still steam being produced and the vent closed after the steam initially filled the radiator, why would their be air ahead of it if the boiler was still running and didn't shut down as of yet.

Brad White_200

I edited it

Hi Betty, I edited it to expand on what would be happening at the same time.

I am not entirely sure what you are experiencing, so am projecting a bit, I admit.

But when a steam system is in operation, each radiator and it's associated air vent, may well be doing different things, depending on it's venting rate and dynamics of the system.

Vents on different radiators are known to sip and gulp air, then vent as the steam within them fills, collapses and fills again, all while under steam. A radiator full of steam can collapse quickly in a colder room, to 1/1700th of the steam's volume. This draws a vacuum which again draws steam.

Ideally, the vents all want to be sized for simultaneous heating, but the reality is a bit of a discordant concert sometimes. I hope that makes sense.