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Interesting dilema

Jeff PerryJeff Perry Member Posts: 86
Was at a job today where we were hired to remove a cast iron rad so they could renovate. While we were at it owner had us replace the rad with one slightly smaller. Renovation is done so we connected it up and tried to fire it up today. The entire zone has no flow. (Technically we don't know if it had flow before we started this project).

Now..... some history. I replaced the boiler almost 30 years ago when I was working for a large company. At the time I was head of the hydronics dept. We installed 2 boilers. Primary/secondary. 6 zones. Cast iron radiation. Monoflo piping. Outdoor reset. I remember that the last time I was there 25+ years ago, everything worked fine.

The zone in question is original to the house. 1-1/4" steel with B&G venturi tees. Tees on the return of the rads. I have confirmed many times over it's not air. There are no high points in the piping. Dedicated risers off the main straight to the 2nd floor to each rad. Assumed it was a circulator issue. Replaced it today. No difference. No flow in any of rads. Got to following the main. By the way, the main is hot as hell. As I follow it around I see a set of tees where a rad was removed. We did it 30 years ago and the 2 tees are connected together with a jumper pipe. However, as I follow the main around I see 5 sets of tees where rads have been removed and installed onto a new loop to make a seperate zone. The old rad hookups are just capped. So now this 1-1/4" main only has 3 rads connected to it and it runs all the way around a large portion of the basement. Even though the 3 rads are right near the boiler they left the entire main and capped the pipes.

So the only thing I can come up with is the capped venturi tees are affecting the flow so much I am not getting any up to the rads that are still connected. By the way, when I replaced the circ (which was a Taco 0010) I first tried a 3-speed 0010 and then tried a 3-speed 00R. Neither pumping characteristic made a difference.

Any thoughts?



  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 2,505
    High pressure drop

    which end of the main are the three radiators connected to? Begining or end?. I suppose they could be in the middle as well. With all those branches capped the main has a high pressure drop as some of the flow used to go through the radiators but is now all being jammed down the main.

    I would think the rads would work if connected to the begining but if near the end?? Can you put some gages on and check the pump with a pump curve?/ May be running at shutoff head. I would have thought the larger pump would have helped.

    i guess the only thing to do is check sizing, pressure drop of pipe fittings and venturi tees and recalculate to find the problem.

  • unclejohnunclejohn Member Posts: 912
    This may help

    Removing Radiation From Monoflo Systems

    An issue we can run into with these systems is when we want to remove a section of radiation. We cannot just remove a section of radiation and cap the lines. We must either remove the tees and install a section of pipe the same size as the main pipe or cut off the vertical risers and connect them together. If we do not remove the tee's or connect the riser it will affect the flow in all the radiation in the system. Remember as we reduce system flow we reduce the heat output from the system
  • Jeff PerryJeff Perry Member Posts: 86
    Yep, I know

    If you read my post you will see I mentioned I had done exactly that 25 years ago to a radiator connection on that loop. Question that was being asked was whether people felt if you cap enough connections off without installing a jumper it would stop flow to remaining rads altogether.

  • stalstal Member Posts: 7
    I had

    the same problem when I bought my house a couple years ago.  The first floor convectors are piped via a monoflo system.  I had converted from oil to gas heat and when the plumber replaced the boiler, he didn't notice that there were two sections that was capped.  I happened to notice it while doing some electrical work in the basement.  I shorted out the t's myself with half inch pipe, but to my disappointment  the pipe i had installed remained cold when i turned the boiler on.  I had a hunch that air was trapped in the pipe, so i re-piped it and added a coin vent so I could vent the air out.  That worked and the pipe gets hot when the boiler runs and my boiler does not short cycle like it use to.  If the pipes to the shorted out t's that you installed remain cold when the boiler is on, I suggest you add a coin vent.
  • SWEISWEI Member Posts: 7,356
    Outdoor reset

    almost 30 years ago was more than rare here in the US.  I'm curious what the setup was?
  • Jeff PerryJeff Perry Member Posts: 86
    Always do

    You always have to be aware of potential air traps.
  • Jeff PerryJeff Perry Member Posts: 86

    Multiple boiler control. Has outdoor reset built in. Don't remember the number but I do remember I started using them fairly early on when they opened for business. So maybe we are not talking 30 years but it's damn close. I seem to remember Tekmar entered the scene in 83 or 84. Control still works fine. Either that or I added it at a slightly later date. I don't remember. I really don't have that many brain cells left. Sniffing too much primer and glue in my life.

    That's my story and I'm sticking to it

    Jeff Perry
  • sdcsdc Member Posts: 12

    How fast is the main heating? Is it possible you have a have a restriction in the main or maybe a valve didnt open all the way? Pressure check at the circ to ensure flow. Good luck
  • sdcsdc Member Posts: 12

    How fast is the main heating? Is it possible you have a have a restriction in the main or maybe a valve didnt open all the way? Pressure check at the circ to ensure flow. Good luck
  • sdcsdc Member Posts: 12

    How fast is the main heating? Is it possible you have a have a restriction in the main or maybe a valve didnt open all the way? Pressure check at the circ to ensure flow. Good luck
  • sdcsdc Member Posts: 12
    edited December 2012

  • SWEISWEI Member Posts: 7,356

    Gotcha - makes sense now.  Must have been a big project at the time.
  • Jeff PerryJeff Perry Member Posts: 86
    Yep, we do

    have a restriction. 5 of them as a matter of fact. 5 monoflo tees with plugs in them. There are no valves except for ball valves. There is a B&G flow control but I manually opened it. Main heats relatively quickly considering the circumstances. No zone valves.

    I've emailed the GC and told him we need to repipe this. We'll see what happens.

  • VPVP Member Posts: 12
    I'm thinking

    we discussed this on the phone already  :)

    HA.  Couldn't resist posting something.....
  • ChrisChris Member Posts: 3,056
    edited December 2012
    Ok Jeff I'll Bite

    What goes into a tee must leave a tee but in this case you have NYC grid lock. You know what to do..For all asking about the restriction, its a MONO FLOW TEE...
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • IronmanIronman Member Posts: 3,550

    5 restrictions and there may be some debris or sludge lodged in one of the orifices which would compound the problem.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • icesailoricesailor Member Posts: 7,265
    I just don't flow:

    I don't know, I've been following and thinking on this for a while. I've seen a lot of missing Mono-Flows in my time and they never acted like that. And when the water was flowing and hot in the main, no matter how slow, the risers and radiators got hot.

    I had a large two story house that had heat installed in the early 60's. HB Smith boiler, and radiators. All on one zone. The main was split in the common way of the day. 1 1/2" main, splitting to 1 1/4". I took it on about 18 years ago. It worked fine. It had a Series 100 running the whole show. All kinds of modifications had been done to the radiators, locations and such. I split the main into two with 2 Taco 573 Zone Valves so you could control either half of the house. I replaced the boiler, and replaced the series 100 with a Taco 007. Like everyone did. It worked fine. But there was one bedroom that the owner never complained about but renters did that the radiator didn't get hot and the room was cold. There were three other radiators with the handle stops missing.  A few years ago, when the owner complained and venting nothing but water, and the radiator got warm, I found that there were numerous Mono-Flow combinations in the mains that weren't connected. And the radiator that didn't work had no Mono-flow, but there were three unused ones within 6'. I connected one riser to a mono-flow and the radiator then worked.

    In the almost 50 years, the radiators all worked. Some would figure that the 007 was grossly undersized. But it worked.

    1 1/4" Mono-Flows have a pretty large orifice hole. It would take one large hunk of crud to block it. Regardless of which way the orifice faced, water would still divert. If you left the flow valve open, it should and would flow on gravity and everything should get hot. I think that something is being overlooked in plain sight.

    The only way I can see that the risers wouldn't be working is if the radiators were removed and not capped off. Demo guys ripped down plaster and got debris in the pipes. Or it was plastered and plaster was dropped down the pipes. I've had that happen to me. No matter what, it should flow on gravity and get hot. Any possibility that a gate valve has a wedge gate that dropped off?

    I've just seen too many orphaned Mono-flows that didn't affect a system to believe that this is the problem. Hydronic systems are just too forgiving for it not to work.

This discussion has been closed.


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