Help with a one-pipe system

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Old 12-21-13, 09:29 AM
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Help with a one-pipe system

I bought a home during the summer months and briefly tested the heating system during the home inspection. The radiators started to get hot, so an assumption was made that the system worked. Winter came and a realization was made that it did not.

The home was built in 1945 and was plumbed with a one-pipe system. Renovations were done within the last decade and two additions were added and they were each zoned separately with a two-pipe system. Both of those zones work fine. A new boiler was installed and I have had the system checked out and they say the system needs re-piped. Just completed major renovations myself and do not want to go that route if possible.

After a system cool-down and flush, the one-pipe zone (zone 1) heats for the first 20 minutes or so and then each branch starts to cool down and never heats up again. One circuit stays hot for along time. It is the 5th bypass circuit. There are 6 bypass circuits total on the one-pipe zone.

The supply and return end of the one-pipe system get hot and remain hot while the zone is active.

The bypass circuits use a monoflo tee and another tee that I have no idea what it is. I am including a picture of one of the bypass setups and a closeup of the tee in question.

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For each bypass, the feed is hot to the radiator but cold throught out the radiator and cold all the way the the return tee. The return tee is hot.

Can anyone give some advice or tell me what this tee is? It is larger than a standard monoflo tee. Cannot find it on the web.
 
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Old 12-21-13, 09:42 AM
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Welcome to the forums...




Its just an older style monoflo tee... Have you bleed air out of the rads?

What is the psi and temp say on the boiler gauge?

Whats the make and model of boiler?

Can you take a pic or two of the boiler?
 
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Old 12-21-13, 10:03 AM
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I have had the system checked out and they say the system needs re-piped
I wonder what lame-azz reasons they gave you for making that proclamation?
 
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Old 12-21-13, 10:51 AM
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For each bypass, the feed is hot to the radiator but cold throught out the radiator and cold all the way the the return tee. The return tee is hot.
Sounds like air trapped in the rads.

One-pipe monoflo systems are notoriously difficult to purge. In many cases, each heat emitter circuit has to be be manually bled, sometimes more than once.
 
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Old 12-21-13, 11:23 AM
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Those look to be awfully small branch pipes leading to the baseboard convectors. That will increase the difficulty of bleeding.

Try bleeding with the pump running and with the pump off. It will likely take several cycles of bleeding each and every convector to get the majority of the air out of the system.
 
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Old 12-21-13, 03:36 PM
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If the runs go downhill you may not ever get it bled without some changes, like purge valves.
Goto comfort-calc.net choose General hydronic sand scroll to monoflo system there are two links and view the second.
 
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Old 12-21-13, 07:57 PM
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I keep thinking about this pic:


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Is that a bleeder valve? If so, I'm confused as to the way that it is incorporated into the monoflo branch....?
 
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Old 12-22-13, 09:56 AM
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That is an odd looking 'thing' to see under a floor! If that IS a bleeder, how will it be accessed after the flooring is installed?

I downloaded and enhanced the contrast of the pic, but there's not enough resolution to tell exactly what that is.
 
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Old 12-22-13, 10:37 AM
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Looks like an AAV.....


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Old 12-22-13, 10:50 AM
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Looks like an AAV.
If it is, then it's a miniature one the likes of which I've never seen...

And also if it is, it's the LAST THING one would want to seal up inside a floor!
 
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