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How to Flush Main lines/returns

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I have a one pipe steam system, parallel flow with dry return. New boiler was recently installed. Based on these photos, can someone tell me the easiest way to flush my mains/returns, without worrying about getting water into the riser pipes and radiators? I think the Hartford Loop piping is confusing me. I'm confused on where to add water and where to drain from. I'm going to insulate all the mains/returns and near boiler piping in the very near future, and just want to give everything a good flush first.


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  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    edited February 2019
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    The ideal solution would be valves on both ends of the wet return, so a hose could be connected to blow any debris out. In your situation, the only easy valve to install would be where the plug is next to the Hartford loop.
    Use a full port ball valve there to avoid plugging up a dinky little valve.
    If you discover you have a liking for piping, I would move the makeup water inlet from the Hartford loop to the wet return to avoid shocking a hot boiler with cold water. In the meantime, throttling the makeup water inlet down would be adequate.—NBC edit-something look back to front with the return piping/Hartford loop, and I’ll have to have a look with my good glasses!
  • JUGHNE
    JUGHNE Member Posts: 11,086
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    Better pictures of return from straight on fm front and straight on from left needed. So no pipes hide behind the others.
  • amitjm1980
    amitjm1980 Member Posts: 33
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    Here's some more photos. Just to save some additional comments, they don't all reflect some updates I have made. The main vents have been turned 180 degrees so as not to collect water. The feeder has been updated to a VXT metered version and the LWCO is no a Safgard instead of a Cyclegard.




  • amitjm1980
    amitjm1980 Member Posts: 33
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    @nicholas bonham-carter I'm assuming the way it is now, there's no way to flush water through the whole loop since I don't have a valve on both return ends? Looks like I'll have to fill with water, then drain?
  • Fred
    Fred Member Posts: 8,542
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    You really never need to flush the mains out. They only see steam and a little condensate so there won't be any debris in there.
    You have an auto fill on the boiler son you shouldn't have to add water. That device (black box with the digital numbers will add water when needed) If for some reason you need to manually add water, use the yellow handled valve on the lower left, next to the auto feeder. That will bypass the auto feeder and add water. Unless you have a valve or plug on the far end of the wet return (along the floor, you really can't flush the wet return.
  • ethicalpaul
    ethicalpaul Member Posts: 5,757
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    But hey @Fred doesn't that feeder have a manual feed button on it that will let it feed AND track the gallons on the nice display?
    NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
  • Jamie Hall
    Jamie Hall Member Posts: 23,527
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    Completely agree with @Fred -- there is no need to flush the mains out, nor the dry returns. The wet returns, they can and perhaps should be flushed -- if you are having problems with slow return water.

    But I think that that feeder does have a manual feed button...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Neild5
    Neild5 Member Posts: 167
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    Question for the pros, is the valve on the wet return feeding the hartford loop an issue? If it gets accidentally closed won't that cause the system to flood?
    WillNH
  • Fred
    Fred Member Posts: 8,542
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    @Neild5 , if he has a spigot at the other end of that wet return, the valve on the Hartford loop would allow him to close it when he flushes the wet return without blowing crud into the boiler. Some also put a valve on the Hartford loop so that they can isolate the boiler (if there are valves on each main) so that some pressure can be built to blow the boiler out without damaging the main or radiator vents. If the homeowner is concerned that kids or someone might close the valve, he could take the handle off and hang it somewhere in the area.
  • Jamie Hall
    Jamie Hall Member Posts: 23,527
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    Neild5 said:

    Question for the pros, is the valve on the wet return feeding the hartford loop an issue? If it gets accidentally closed won't that cause the system to flood?

    Yes, it would. Which is one reason why it, like everything else on the boiler, is to be manipulated only by those who have some idea as to what they are doing and why.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 11,086
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    Your wet returns only amount to the pipe lying on the floor, looks to be less than 6' between the left and right dry return drops.
    IIWM, first shut off the power, I would drain the wet return with the hose connection.
    Then remove the plug under the large yellow ball valve.
    I would remove the small hose drain you just used and put a nipple and cap there.
    Where that front plug was I would put a full port ball valve with a garden hose adaptor with brass cap.

    Then with drain hose on the new valve I would use the manual bypass fill ball valve to raise water in the wet returns (and boiler) above the sight glass top and then let it drain. Back washing this back and forth until you get clean water out the hose.

    Then I would drain the boiler thru the right side boiler drain, as some sludge may have washed over the HL into the boiler, add water thru the bypass ball valve and back wash everything again until clean water flows from both drains.

    Important..................Then fill the boiler to the correct level, turn the power on and bring the water to a complete boil to remove oxygen.

    By using the manual bypass fill valve for this you do not add any gallons to the readout on your water meter. You are at zero now and any future readings will be water lost somewhere else as the loss should be very minimal.

    While it is drained you might consider the full port ball valve on the boiler drain. All these threaded fittings will become more difficult to unscrew as time passes. That explains why a nipple/cap is preferred over plugs.
    If you remove it and look at the opening size you will realize how slow the flow would be thru that port.
    The larger port will flow more sediment out with the increased volume/velocity.

    The large yellow ball valve, if off would not allow water to return to the boiler. It would stack up in the returns and your water feeder would keep adding water.
    If you had a drain hose connected then the returning condensate with steam pressure behind it would flush out the returns. I would leave it open until you wanted to do that, then I would remove the handle and hang it on a nail near the boiler.