Fixing the gurgling at the end of my Steam Mains

" The only problem is that I get a lot of gurgling, bubbling sounds at the far end of the house from the boiler. It happens on a cold start and goes away within a few minutes of the radiators getting hot. "

From a cold start, if there is some trapped water in various parts of the system the moving air trying to get out of the system through the vents may bubble through and/or push the puddled water around and along. Once the main vents close that flow is dramatically diminished and is mostly just condensate flow (not much sound).

The majority of the steam then goes to the radiators and condenses, the condensate then fills up the low points again and waits for the next cycle. Correct the poor piping techniques (lack of an Eccentric Reducer or other appropriate technique) and add pitch if possible.

You said it is a two pipe system, the condensate end of each radiators drops down to the wet return ?

I like a little hisssing and gurgling. It lets me know the house is alive.

If those drips go below the water line, traps on those lines are a "won't help and WILL hurt: item. Don't do it. Don't let anyone else do it.

The gurgling you hear is, as has been said, almost certainly condensate trapped in low areas on the piping. The guys have pointed out some locations which are suspect.

Zoro and Ferguson have them. Kinda pricy.

Google Anvil eccentric reducer.

After you get all the crud out that is possible and assuming that both returns drop into a wet return pipe before rising up into the Hartford Loop return, you could:

Add a valve to isolate the wet return from the boiler and add a full size drain valve to the lowest point on the wet return.

Then run the boiler in the "no return" mode. This is shutting the valve to prevent any return going into the boiler. Open the new drain valve to waste the return water down a drain. You will have to monitor the water level in the boiler as you do this.

The wet return at the boiler also performs as a "P" trap and is where any crud from the return lines will collect. Your "no return" mode will flush the returns.

If you go to the "Silent Steam" U-tubes by Gordo S. you will see that they often do that with a new boiler install.

After some operation, just draining the wet returns with the drain valve will remove more debris before it gets into the boiler.

Also remove the handle from the valve that isolates the returns from the boiler when finished with the no return operation.

The drain port needs to be on the lowest point of the wet return piping to keep the crud out of the boiler.

If you rely on the boiler drain itself then the crud will settle into the bottom of the boiler and not get out, especially with a small drain tap.

Check out the U tube by Gordo.

The full port isolation and drain valve goes at the low point of the wet return just before the Hartford loop, you don't want to push the debris into the boiler during flushing. As @JUGHNE stated, it may make more sense it you watch some of the Youtube ''Silent Steam Team" boiler install videos where @Gordo explains the wet return flush setup.

As far as a scraper, I'd probably start with a piece of 1/4" or 5/16" all thread (3 foot long) an make a half circle scraper out of metal or heavy plastic and double nut it on the end of the all thread, The all thread can be extended if needed. The flush hose may fit over the top of the half circle scraper.

Yeah, I'd probably use what you have, certainly better than not doing it at all. Full port valves just give better flow, in your case you could just let it run longer, if needed.

They Both look easy to change (threaded) if you wanted to. The Red handled drain valve is probably a ball valve, may not be full port.

You could flush from Blue to Red then the other way too.

I think we've all done that sort of thing at least once…

Oops, one problem solved, made another, S#it happens. Quick 'pressure washer' the evidence away, No Don't, it will probably make a bigger mess.

I like it, it should drain good. Maybe the only thing I would have done differently is put the vents in a place with better access. Maybe it is not as awkward to get to them as the pictures look to me.

I was thinking something like this. But maybe it looks better from here.