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Bosch Greenstar Combi with excessive exhaust / Intake condensation

TroyMn
TroyMn Member Posts: 3
in THE MAIN WALL

Hi - I'm very new to this group and boilers in general. I'm hoping someone can help me out. I have a Bosch Greenstar ZBR 28-3 combi boiler. It was installed in 2015 for in-floor heat and DHW. About 5 years ago, I noticed water inside on the bottom of the cabinet. I thought it was coming from high on the back of the heat exchanger but I could not tell for sure. I cleaned the combustion side of the heat exchanger and the problem seem to go away. This year, I ordered a gasket kit and cleaning brush because I knew it was due for cleaning. I brushed out the heat exchanger, replaced the flame sensors and put everything back together. All is running smooth but I have excessive condensation in the intake / exhaust at the top of the unit causing water to pool on the bottom of the case (red arrow on photo is where the condensation is forming ). I have a concentric intake / exhaust and everything seems Ok with no obstructions. I can see steam blowing out when the unit is running. When I was cleaning the heat exchanger, I inspected the exhaust blower and blew it off with compressed air. All seemed OK with it. I can hear the blower running and it is pushing exhaust outside. Based on the rust build up on the inside bottom of the case, I'm guessing I have had this problem for a long time. I know it is not correct to run the unit without the cover installed but when I do, the water accumulation is less. Obviously, I should have been better with maintenance early on but I didn't know any better - I'm learning. Any help would be greatly appreciated.

Overview.jpg
Exhaust01.jpg

Comments

  • Ironman
    Ironman Member Posts: 7,695

    Replace the flue connector: it’s leaking between the pipes.

    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    GGross
  • kcopp
    kcopp Member Posts: 4,531

    I would ditch the concentric vent.

    I have seen a lot of cross contamination w/ these.

    Typically happens at low fire vs. high fire.

  • TroyMn
    TroyMn Member Posts: 3

    Well, Ironman, I think I owe you lunch. As I was disassembling the flue connector, I could feel water above it and the rust didn't line up. I'm guessing the installer twisted the top adapter and broke off both inspection ports. When I tried to loosen the plugs, I could feel them just spinning When I got it apart, they were both broke. From what I can tell, this is where the condensation was coming from. I'll know tomorrow when I get it back together.

    PVC Port.jpg
    IMG_3542.jpg
    kcoppGGrossIronman
  • GGross
    GGross Member Posts: 1,466

    Wow the ones I have messed with it would pretty difficult to break off those inspection ports. You may be able to rig up a temporary plug for them just make sure anything you use is rated for the temperature

  • TroyMn
    TroyMn Member Posts: 3

    I used a thin strip of aluminum (appropriately cut from the side of a beer can) to cover both holes and some temp rated epoxy. Everything went back together and all seems to be running without issues. Thanks again for the quick help. I'm recently retired and have a bit more time on my hands so I may start a new thread on what would the best settings for this boiler. I'm guessing the installer set it to the "never call me again" setting. Thanks again!

    GGross

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