Help! Two-pipe system in Manhattan with hammering / banging pipes

Startover

Looking for advice and expertise. I live in a coop building with loft apartments in Tribeca. Building is 90+ years old. Am on the second floor--about ten floors above me, and retail space below. I am the only one hearing clicking, banging and pounding. Especially at night / when it gets cold. One return pipe in particular is 90% of the noise. The rest 10% from two of the other four return pipes in my unit. You can also hear water gushing through it, and not just at the end of the boiler cycle of 1 hr 40m. And that riser gets lukewarm at best, while the other return pipes get much hotter. The banging is most pronounced for about 5-7 minutes in each cycle.

We have checked and replaced old traps in the apartments above me. Will likely replace the traps or elements for radiators in the retail space below me, although they seem to be working fine. We got a plumber to attach a hose to the top of the offending pipe in my unit and drain it of water and air. That helped but maybe just for a couple of hours ... the banging started again. We also tried changing the pressure in the boiler (from 4 down to 2.5) but it seemed to make it worse. The vertical riser terminates in the store below, and then wraps around horizontally. Getting to the horizontal section will require breaking open the ceiling in the store. We are running out of options besides replacing the elements of the radiators in the store and maybe cutting open and draining the riser in my unit and cleaning it below where the hose we attached could access.

This problem has been confounding us for weeks. Anyone have any prior experience or creative ideas? The less invasive the better. Thank you.

Startover

I meant to also say, the problems is 5x worse than prior years when it was more clicking than banging.

JUGHNE

Can you see the boiler pressure gauge reading when steam is up?

Also the pressure control settings on the face of those controls?

Jamie Hall

If you were able to drain any water out of that riser... there's your problem. It has a pitch problem somewhere, or it just might be double trapped.

Mad Dog_2

I'm here to help, sir.  Mad Dog 

Mad Dog_2

We can come and do a Field Visit and give you a clear picture of what is wrong and how to fix it.  Approaching 40 years diagnosing and fixing screwed up heating systems. Mad Dog .