Help diagnose radiator noise

holograham

I am a bit stumped here. 

Single pipe steam system. 45% oversized boiler. Fully vented mains. Recently cleaned and skimming boiler. Mains not insulated (going to insulate next week). Near boiler piping incorrect but not the worst. Likely results in some wet steam.

Happening on 2nd floor American Radiator Co. Peerless two column- 23inches tall, 22 sections, 51.33 EDR. Pitched correctly. In a radiator cover box. New Gorton 4 vent (room gets hot so venting slow) which replaced a decrepit ventrite (made same noise with ventrite). Noise happening at end of boiler cycle (so pressure is building before pressuretrol cuts off). Typically doesn’t happen on the short cycles (usually have 2-3 pressure cycles after the initial 40 min cold start).

Would say it’s pressure or wet steam related but why the only radiator making this noise?

https://youtube.com/shorts/X34p2mh_JuM?feature=shared

Steamhead

Water is backing up in the rad. That causes the gurgling we hear. I bet the shutoff valve disc has broken off the stem, which blocks the returning water.

holograham

Steamhead said:

Water is backing up in the rad. That causes the gurgling we hear. I bet the shutoff valve disc has broken off the stem, which blocks the returning water.

Other than the noise - is this urgent to fix? I forgot about the broken valve disc potential.

Steamhead

Not life-threatening, but it could make the vent spit and of course the noise is quite annoying.

holograham

Ok thanks - yes vent is spitting and is brand new. You can hear it at the end of the video. 

holograham

As an update here - had the valve replaced and the noise completely stopped. Perfect now!