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Main vent failing

We have a new residential customer. He says one of his main vents has failed 3 times in the last two years. I went out to look at it yesterday. The vent has obviously been leaking. It's a 75.

They have to loops around the basement with a main vent on each. Both are about 14" back from the drop. From the elbow the return is 1" copper into the slab. Both returns must Tee somewhere under the slab, because at the boiler it comes out of the floor 1 1/2".

I could offset the main to see if that helps, but I'm thinking the one return may be blocked under the slab. How can I test it, or flush it? BTW, there are no drains in the floor, and no valves to isolate the individual returns.

Comments

  • dopey27177
    dopey27177 Member Posts: 872
    If this is an old building replace the underground piping as it may be short lived.
    I do not know what the original pipe size in the building is but the drop pieces should be full size, the underground for 1 loop can be 1" at the meeting point for both 1" returns a 1x1x1/4 copper t can be installed and 1 1/4 line can be run to the boiler. All or most of the piping should be done above ground or if installed under ground be covered with sand no broken cement or rocks, Where the pipe goes underground and comes back out of the ground install PVC pipe sleeves.

    I think that the 1" drop is not allowing all the condensate to drain out of the 1 1/2" pipe.

    If the steam main is not insulated additional condensate is produced and that condensate water will stack up in the steam main and shock the vent valves.

    Three things can be done:

    Make the drop piece 1 1/2" and reduce the size at the wet return
    or insulate the steam main and near boiler piping if needed
    and clean and flush the wet return and lower inlet return tapping into the boiler. There can be dirt in the piping impeding the return of water into the boiler.
  • ethicalpaul
    ethicalpaul Member Posts: 3,739
    For testing, you can remove the vent and pour water into the return then see if the water level in the boiler rises (and how fast). It should rise almost immediately as you are adding water (you may need a helper).

    Try it on both mains. If one is slow, and the other is fast you know a blockage might be before they join. If they are both slow, the blockage might be after they join (not necessarily that helpful to solving it).

    To flush them I think you will have to maybe add valves and/or tees to the returns on the incoming and outgoing sides, but some pros might have some better solutions there.

    Or you can cut off and abandon the buried returns and just run new ones at the surface. Buried returns are one of the worst ideas in hydronics IMO right up there with DHW coils in boilers.
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
  • Steamhead
    Steamhead Member Posts: 15,329

    For testing, you can remove the vent and pour water into the return then see if the water level in the boiler rises (and how fast). It should rise almost immediately as you are adding water (you may need a helper).

    Try it on both mains. If one is slow, and the other is fast you know a blockage might be before they join. If they are both slow, the blockage might be after they join (not necessarily that helpful to solving it).

    To flush them I think you will have to maybe add valves and/or tees to the returns on the incoming and outgoing sides, but some pros might have some better solutions there.

    Or you can cut off and abandon the buried returns and just run new ones at the surface. Buried returns are one of the worst ideas in hydronics IMO right up there with DHW coils in boilers.

    This.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    Paul Fredricks_3
  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557
    I did suggest insulation as none of the pipes are wrapped. The house was built in 1941 so I would assume the original returns were steel. They are copper now. Running new returns above the floor would put them in bad locations in the basement.

    I will probably tell him to insulate the pipes and see if that alleviates the issue. It has to be done anyway. Flushing will take quite a bit of pipe work.
  • ethicalpaul
    ethicalpaul Member Posts: 3,739
    edited August 2021
    Not to contradict Jake but IMO the additional condensation caused by an uninsulated main is extremely minimal in the scheme of things. I don't foresee a meaningful change in your system from it as relates to this issue.

    Probably more work than any normal homeowner will approve, but I put a sight glass where my main drops to the wet return. I put it just above the normal water line level, so if the level rises (normally due to pressure in my case), I can instantly see it.


    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    Paul Fredricks_3