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How to drain/ fill/bleed old boiler and forced hot water system

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Hi all, thanks in advance- you have been so helpful in the past. I am replacing a taco 110 Bearing assembly. Could anyone help with the steps involved in draining, filling and bleeding the system? Its a 1940s-50s oil fired boiler with radiators in a two story house. Thanks!

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  • hot_rod
    hot_rod Member Posts: 22,341
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    draining should be simple enough if there is a boiler drain at the boiler bottom.

    Only drain down to the level of the work you are doing.

    Does the system have a pressure reducing fill valve?

    Purging depends on how it ids piped, where valves are located. a pic or drawing would help.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    hockeyman70s
  • mattmia2
    mattmia2 Member Posts: 9,837
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    Also depends on if there are isolation valves for the circulator or at least for the system loops.
    hockeyman70s
  • hockeyman70s
    hockeyman70s Member Posts: 18
    edited October 2022
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    hot_rod said:
    draining should be simple enough if there is a boiler drain at the boiler bottom. Only drain down to the level of the work you are doing. Does the system have a pressure reducing fill valve? Purging depends on how it ids piped, where valves are located. a pic or drawing would help.
    @hot_rod  @mattmia2  Attaching a few pictures. I have 2 valves I would think might drain the boiler labeled “1” and “2” in the picture. There is also a valve at the bottom of the hot water tank. I have also attached a picture of the following valve assembly's (haven’t ever really played with them). There aren’t any valves near the leaking circulator pump to isolate it that I can see. I have also attached a picture of the two valves w/ hose attachments at the end of the two zones I would guess that I will bleed from?
    thanks!
  • JUGHNE
    JUGHNE Member Posts: 11,089
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    Could you show how your hot water tank is connected to your boiler and what pump feeds it?
  • hockeyman70s
    hockeyman70s Member Posts: 18
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  • mattmia2
    mattmia2 Member Posts: 9,837
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    Oh. the indirect is separate, it is heated through a tankless coil and there is a bronze circulator that circulates potable water through the tankless coil.
  • mattmia2
    mattmia2 Member Posts: 9,837
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    Valve 1 drains it. trying to get the air out of it could be..interesting.
  • hockeyman70s
    hockeyman70s Member Posts: 18
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    @mattmia2 thanks! I did it yesterday. I did drain from valve 1. bled off those two valves pictured on the ceiling and then bled every radiator. I am seeing a slightly higher boiler pressure since but may try rebleeding the radiators.
  • mattmia2
    mattmia2 Member Posts: 9,837
    edited October 2022
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    Is there a compression tank up in the ceiling somewhere?

    Er, with the air scoop and automatic vent it should be a diaphragm tank.
  • mattmia2
    mattmia2 Member Posts: 9,837
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    Never mind. i see in the first picture the air scoop goes in to the compression tank. You might need to close the isolation valve to the compression tank and drain it.
  • neilc
    neilc Member Posts: 2,711
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    mattmia2 said:

    Never mind. i see in the first picture the air scoop goes in to the compression tank. You might need to close the isolation valve to the compression tank and drain it.

    and with compression tanks,
    you do NOT want any auto air vents left open if present, you'll end up loosing your air cushion in the compression tank.
    you can use the auto vent when first filling, but before the circ starts, close the air vent(s),
    known to beat dead horses
  • hockeyman70s
    hockeyman70s Member Posts: 18
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    @mattmia2 @neilc thank you guys! I did just shut off the feed to the compression tank. Emptied it completely and then opened the feed line back up. Upon reheating the pressure is back up at 19-20. I may try it again but this may not have been it.
  • neilc
    neilc Member Posts: 2,711
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    you look to be another system pumping towards the tank, the PONPC,
    and your feed is piped into the suction of that nice big circ,
    so let's say you want 12~15 at your tank, for a system static fill,
    circ differential pushes to the tank, let's say 15/20psi, the tank levels it out to 12~15,
    but on the suck side of the pump, you're pulling in 5/10, more or less,
    what's that 12psi feed gonna do?
    (these are all just approx #s, )
    so you pull on the feed until the 12 is satisfied on the suction side of circ,
    and your system balances out around 20,

    that all said, 20 isn't the end of the world,
    as long as things aren't leaking,
    and as long as it doesn't creep past the 20,
    if you approach 30 you'll start testing the relief valve,

    if you know you're not leaking,
    shut the fill valve off and keep an eye on the system pressure,
    that it doesn't leak down,

    but wait, there's more,

    you said you drained the tank,
    are you sure you let air in? and got all water out?
    did you hear the glug glugs?
    cuz I can't see that drain so well to say it has the incorprated venting , , ,
    known to beat dead horses
  • hockeyman70s
    hockeyman70s Member Posts: 18
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    Thanks @neilc I did drain it down and heard the glugs! Im still a novice with plumbing/ heating stuff but am handy and a decent learner. Before draining the system/ swapping the circulation bearing assembly and refilling and bleeding, the pressure was roughly 16psi @150 degrees (not actively running). The system is an antique and cant imagine most of the pipes are a heck of alot newer. Hoping to keep pressures as low as possible to stave off any undo stress.
  • mattmia2
    mattmia2 Member Posts: 9,837
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    Was the house built in the 40's or 50's when that boiler was made? It kind of looks like it is the second boiler.
  • joeba
    joeba Member Posts: 24
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    I know that this system has been working for a long time, but the one thing that sticks out (besides the circ pump location) is that there is not enough straight pipe entering the air scoop so It probably not eliminating as much air as it could.
    hockeyman70s
  • hockeyman70s
    hockeyman70s Member Posts: 18
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    @mattmia2 It was a carriage house/barn for who knows how long but converted into a house in the 50s. Not too sure what you mea by second boiler.
  • mattmia2
    mattmia2 Member Posts: 9,837
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    I mean that boiler was a replacement for the original boiler, but if it was converted to habitable space in the 50's that boiler and the system were probably installed at that time. The piping is larger than it needs to be for a system with forced circulation so I was wondering if it was a converted gravity hot water system.