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Indirect water heater getting airbound... looking for advice

markp1markp1 Member Posts: 56
This past weekend I had a Viessmann boiler and a Superstor indirect water heater (IWH) installed. The IWH is plumbed before the low loss header (LLH). As the LLH has the air vent on top of it, the circulation path of the water from the boiler to the IWH and back does not travel through the LLH, so any air cannot make its way out.
The IWH has become airbound three times now in 5 days. I purged the system of air each time, but it still continues to get airbound. I have attached a picture (pipes are not bent... I used a panoramic shot to take the picture as the boiler is on a wall 90 degrees to everything else), and drawn on the picture the flow of water for the IWH. Additionally, after a few days I can hear any in the boiler as well.
Any advice on how this can be fixed to eliminate the air in both the IHW and the boiler?

Thanks in advance,


  • SWEISWEI Member Posts: 7,356
    Can't quite tell from the photo, but it looks like both circulators may be pumping towards the expansion tank. Do you see any water near the drain pipe attached to the PRV?
  • markp1markp1 Member Posts: 56
    The expansion tank is on the outbound side of the boiler, and both pumps are pumping into the boiler. There is no water near leaking anywhere in the boiler plumbing area (PRV included).
  • hot_rodhot_rod Member Posts: 13,882
    here is one suggestion for the expansion tank connection.

    And the latest issue of idronics related to Separation in Hydronic Systems.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • markp1markp1 Member Posts: 56
    That's interesting... so the expansion tank goes on the return of the system side before the low loss header.

    So the point of no pressure return (PONPR) would never have water passing by it when the IWH circulator is running...
  • icesailoricesailor Member Posts: 7,265
    edited October 2014
    I have done a few Veissmann Vitodens I looked at my old saved PDF's for the piping. I have never seen any old Vitodens drawn like that. Every drawing I have ever seen (and unless it has changed,), has the low loss header, and the primary pump as one circuit with the primary pump pumping directly into the boiler. There is no indirect water heater piped between the boiler pump and the boiler. LL Header separates the Primary and secondary.

    Every old drawing I have seen has the Indirect connected AFTER the LL Header connected to the secondary side of the primary/secondary side. It sounds like you don't have proper flow through the primary side and it is by-passing and boiling in the HX. If you have the installation manual on site, plan 2, 3, and 4 do not show anything like that.

    You have to follow the manufacturers engineered drawings.

  • markp1markp1 Member Posts: 56
    Per the B2HA manual, layout 2 shows the indirect water heater connected before the LLH. What isn't followed according to layout 2 is having the expansion tank between the LLH and the boiler pump... so if I move the expansion tank to be between the LLH and the boiler pump, the install would match layout 2. Do you think that would be enough to eliminate the air issue?
  • kcoppkcopp Member Posts: 3,538
    edited October 2014
    stupid question....can you put a air separator in the line to the Indirect wh? And the boiler loop circulator...that looks like a really old Taco 007.... circa 1980's
  • jonny88jonny88 Member Posts: 1,139
    I am with kcopp here.When I pipe an indirect I like to use a caleffi auto air vent on supply and return of indirect piping usually takes care of any air issues
  • icesailoricesailor Member Posts: 7,265
    Where does all the air come from?
  • markp1markp1 Member Posts: 56
    Great questions / comments... kcopp, you are right, it is an old Taco 007-F3. Due to needing to get the boiler installed and be eligible for a significant rebate, I had to go ahead with installing before the new Taco Viridian pumps showed up. The good news is that the pumps are arriving late today at my local supply house, so I'll be swapping out the old Taco 007-F3's with the Taco Viridian's this weekend.

    I just did a test this morning, and now realize that the 007-F3 doesn't have an internal check valve... so when the IWH pump is running (a new Grundfos UP15-100F), some of the water is looping up through the boiler pump, into the LLH, and then coming back to the IWH. So the flow through the boiler is much lower than it should be, so it is probably boiling the water in the boiler. If I close the valve by the boiler pump, so all the IWH water flow goes through the boiler, there does not appear to be an issue with air.

    I can add an auto air vent in the IWH loop. As the supply is higher than the return, would it make sense to put it on the supply line going into the IWH?

    Should the expansion tank still be moved?

    Thanks everyone for all the help!
  • SWEISWEI Member Posts: 7,356
    Move the expansion tank and the PoNPC will be where it needs to be to prevent cavitation.

    With pump-based DHW priority, both pumps must have flow checks in them.
  • markp1markp1 Member Posts: 56
    So the new pumps going in this weekend will have the flow checks, so that part will be solved.

    For the expansion tank, I could have it between the LLH and the boiler pump (which would match layout 2 from Viessmann) or I could put it on the system return before getting back to the LLH (would not match layout 2 from Viessmann, but would match the idronics article). Which would you recommend?

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