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Suction tube blockage

I own 20 rental houses and 3 of them have the same recurring problem. There is an aluminum nipple on the draft inducer with a 1/8" rubber hose on it. This hose connects to the vacuum sensing diaphragm switch.



Once a year these aluminum nipples corrode enough to clog, so the furnace locks out.



Everything works again if I drill out the corrosion.



What's the long term solution?
Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments

Comments

  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,510
    aluminum attack

    what about hanging up some strips of aluminum foil near this nipple to see if there is some chemical in the vicinity which is reacting with it?

    a stainless steel nipple could also be found.

    aluminum reacts with a number of things. to generate hydrogen gas [for your next balloon experiment], put aluminum foil into a solution of lye, and water. could there be a washing mashine nearby, or a dried up floor drain oozing sulphur hydroxide sewer gas?--nbc
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Corrosion, yes

    The products of combustion of the furnace apparently cause the corrosion.  It's mainly the water in the flue gases.   The Al nipple is swaged in, so it's not field replaceable.  The new fan assembly is $180, but I'm not sure a new one would have a design solution.



    I could drill them out and put in a brass nipple, I guess, or drill it out to a larger ID that would take longer to corrode shut.  



    I just thought that if I'm seeing this in 15% of all my furnaces, someone on the Wall would have solved the problem by now.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Hose 'em...

    Kevin, the problem is that the Aluminum is "seeing" the condensate of the flue gas. If you put more hose on it, the nipple and diaphragm will not meet the condensate, hence longer life. It may also have something to do with the vertical separation between the switch and the flue connection.



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Timco
    Timco Member Posts: 3,026
    drainage?

    If it is a mod con furnace check that the inducer can drain freely. If 80% unit, find out why the moisture is so high in the inducer. same company put all of them in? Sounds more like venting error because no water should be in there...or enough to clog the connection as you describe. Maybe that is the drain and you need to connect pressure switch somewhere else? Just tossing out suggestions now...I have looked behind a hundred inducers and all are dry with no signs of moisture...



    Tim
    Just a guy running some pipes.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    The nipple's on the draft inducer housing

    The furnaces that corrode are in crawlspaces, so the ambient temperatures are a cooler, which could explain more condensate on the inducer housing. More tube wouldn't help because the bad nipple is on the other end of the tubing from the diaphragm switch, right at the source of the corrosive water.



    The inducer is sucking the flame thru the furnace, so some moisture seems natural. The nipple is at about 2 o'clock, so liquid water should drain out. The diaphragm switches have no trouble at all.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Sorry...

    That's what I get for speed reading...



    Misunderstood your "issue". How about buying a Brass fitting from HD and replacing the albuminium fittin'?



    ME
    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
This discussion has been closed.