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Thrush No. 720 Air Eliminator

This morning I replaced an expansion tank with a journeyman I work with and we installed a Thrush no 720 air eliminator that our boss brought out with the equipment/supplies. We installed the 720 high on the supply pipe and when we turned the boiler feed/boiler on water came spewing out of the top of the 720. Now here is where I am confused...I asked before install, do we need and auto air vent at the top of this thing? Based on the instructions and the journeymans knowledge he said no we dont, that it is the air vent (the 720) Why then when we turned the system on water spewed out all over? The only thing the journeyman said was uh I guess we do need and auto air vent. He also said because its saturday and nothing is opened that it can wait till monday. Now I researched and read the best i could and now im here writing this...if the 720 has a float insiade and the instructions made it look like the whole part is a vent then why did it not work? And why did the journeyman pipe a 3/8 nipple into a ball valve coming out of the top of the "air eliminator"?

I am trying to learn the proper way to do this stuff and this didnt seem right to me, any advice? what should I do?


  • Charlie from wmass
    Charlie from wmass Member Posts: 4,333
    was it installed

    right side up? I am not familiar with these units but the literature looks like the float is built into the unit. It may be dirty or it is just a typical Saturday install, this is why I only do emergency work on Saturdays.
    Cost is what you spend , value is what you get.

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  • Ironman
    Ironman Member Posts: 7,397
    Thrush 720

    When you say water was spewing out of "the top", are you referring to the nipple on the side near the top? If so, that is where a ball valve is supposed to be connected to skim debris from the 720.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
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