Amputated monoflo mystery

Joe_30

We Removed a short little 4 section cast iron radiator from a monoflo system. I connected the risers directly with a few 6 inch nipples and a union. [This rad was always good and hot, but I no longer needed it after I put a larger rad in another corner of the room off other risers.]
I cannot detect any warmth in the little connecting pipe. It rises within the house but turns out into the outside wall at the joist cavity.

Why would the flow stop? Freezing is the concern. I have insulated outside it and have left a vent to the room. Perhaps that suffices. This is Minnesota.

Original system was all buried in-the-wall fin tube 1940 style. There was only 1/8th inch of asbestos and tin foil between rad and sheathing.! I've now used some neat salvaged iron rads that do a much better job and also had a byproduct effect of stoping short cycling of the boiler.They are fully within the heated room .
The removed unneeded rad was a substitute that a prior homeowner had put in but he had failed to go all iron.

There is this: the little removed rad in question and a small iron rad about 18 inches away in a bathroom are served by the same pair of risers.

thanks, joe

Uni R

Monoflo mystery

Do you have a way to bleed that branch from the highest point and have you done so?

Unknown

Like Uni R said

you have to get the air out of the highest point of that piping . Try opening the union a little to burp the air out . But be very careful , the water can get extremely hot .

Joe_30

Darn it, that's it.You're right. That bridge piping between two risers is an inverted U, functionally like a small unvented radiator. I'll bleed the one its twinned up with. And/Or loosen the union in the bridge to let air out. Lastly I could let the system down and try to pressure purge it, but that did not do it on the post-install filling. Funny how the obvious gets away from me . Thanks, Uni R.

Uni R

Amputated monoflo mystery

Good luck... You might want to throw some type of valve in there because you are always going to have to check for air every time you drain anything and most likely once a year when you check the system for air.

Weezbo

add a jomar with a caleffi autoair vent:)

Uni R

Caveat...

It would be best to first ensure that the HO has a bladder style expansion tank before putting any autovents in.

Joe_30

Yep, it needs a bleed valve for sure. Have conventional expansion tank [not bladder type]. Thanks to all. Its funny how things we know [allow for air removal at top of system] escape us in a different configuration situation.