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Thread: Boiler heat tutotial

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    DIY Senior Member jim mills's Avatar
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    Default Boiler heat tutotial

    I'll start by saying that I know almost nothing about boiler heat, except for what I have read in the past couple months. A friend of mine just purchased (against my advice) a large 1920's tutor with boiler heat, and asked me to come take a look. There was no walk through at closing, so they are clueless so to speak.

    I know that the system is a circulating hot water system, probably converted over from steam at one point.

    About half of the cast radiators have been replaced with fin tube and "toe kick" radiators and a large percentage of the smaller (1" & less) lines have been replaced with copper maybe 25 years ago. I hate to see copper coupled to galvanized, but no obvious signs of galvanic corrosion.

    There are two cast radiators that don't get hot. The incoming pipe & valve are hot, but not the radiators. The valves are stuck. I'm guessing that the valve is in the closed position & rusted there. I opened the bleeder & a little water came out, so I immediately shut it. There is a branch (booster?) pump on this branch but the wire has been cut. The pipe is hot on both sides of the pump, so I am assuming that the pump is just freewheeling. I'm capable of replacing the valves, but I just want to make sure I am not getting in over my head.

    I had the boiler guy out, but I was not impressed, he seemed to barely know more that me, and he supposedly "inspected" the boiler just a couple weeks ago, but couldn't find the boiler room or thermostat. Hmmm...

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    There's more than one way to plumb radiators. I may not have the terminology proper, but if you have a 'main' line, and then it T's off to go to the radiators, that is a special type of T that scoops some of the flow into the individual radiator. Another way it is sometimes done is in a loop, where instead of a 'main' line, it literally loops through each unit. With that type of a system, you cannot turn one off, since the flow goes through all, it would block them all, since no water could circulate.

    Over the years, if the boiler saw fresh water added, every time that happens, you introduce some air into the system dissolved in the water, and that means some oxygen, which also means some rusting of the iron components. Ideally, the thing would never leak, and all the rusting would be over in the first week or so. That is the reason why boiler piping and radiators can last a long time...it should be a nice sealed system, with no constant source of oxygen.

    Older boilers tended to be turned on and left on during at least the heating season, and maybe all year if they also provided the hot water to the house either through an internal coil or an indirect WH. The older ones were not designed to be cold started frequently, thus they may bounce between a min/max setting. OFten, the only thing the thermostat did was turn the circulating pump(s) on or off. Newer boilers can have more sophisticated controls, and many them can safely do a cold start, and may not maintain any nominal temperature setting.

    On the boiler itself, it will have some safety features: over temp, over pressure, minimum pressure; along with a high and low temp aquastat.

    Not sure if this helps, but not sure what you are looking for.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    In the trades Dana's Avatar
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    Some pictures of the plumbing, pumps, & valves might be useful here.

    (BTW: Jim- the terms you're probably seeking are "monoflow" and "monoflow tees".)
    Last edited by Dana; 02-14-2014 at 02:23 PM.

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    DIY Senior Member jim mills's Avatar
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    Thanks, I'll try to get some pictures, but there are pipes everywhere! I can tell you that the area I am having trouble with has a "main" line around part of the perimeter of the basement, then "t's" going vertical to the individual radiators. All the supply & return lines are hot, but two of the radiators are cold.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Then, it's likely one of two things...either the T's are not monoflow so they can direct some water into their respective radiators (the pipes will get hot just by some convection and conduction), or the lines, valve, or the radiators themselves are clogged, preventing flow through them.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    Quote Originally Posted by jim mills View Post
    Thanks, I'll try to get some pictures, but there are pipes everywhere! I can tell you that the area I am having trouble with has a "main" line around part of the perimeter of the basement, then "t's" going vertical to the individual radiators. All the supply & return lines are hot, but two of the radiators are cold.

    That sounds like a mono-flow setup. The tees have little scoops in them directing some of the flow in the main line both to & from the radiator:



    You may very well be air-locked out on the loops with the cold radiators and you may need to be shim the radiator a bit higher (to take the high-point out of the plumbing) or find a way to bleed air from that branch.
    Last edited by Dana; 02-17-2014 at 01:41 PM.

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