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Bosch Greenstar Combi 100 / Not sufficiently heating three zones

Help... I had a brand new Bosch Combi 100 installed recently and ever since then it seems that it is not properly heating my three zone home (one zone per floor). The baseboards just dont seem to get as hot as they did with our old boiler. Originally i thought it was the outdoor temperature, but last night is was approx 32F outside and the baseboards just weren't getting warm enough. After reading some of the posts here i thought it could be related to primary/secondary piping perhaps.. Any ideas? Pictures attached.

Thanks a million!


  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    Cold baseboards

    Have you asked the installer about the cold baseboards? Is the temperature setting for radiant floor (lower temperatures), instead of baseboard (higher temperatures)?

    Could the controller be locked into a setback somehow? During times of constant hot water use, the unit will not be heating.

    Was a heat-loss survey done on the house to determine the boiler size? Have you compared the piping diagram in the instructions with what was installed? A quick look seems to indicate some back to front component locations.--NBC
  • Jamie HallJamie Hall Member Posts: 6,653
    And before we start chasing phantoms...

    a rather obvious question: is it just the baseboards which seem cold, or it is not capable of heating the house and satisfying the thermostat?  If it's the latter, it's time to start looking at some of the things NBC was mentioning.  If it's the former, could it be that it is simply running a cooler temperature, but longer, for more efficiency?  That would be controlled by the outdoor reset curve, if it has one...

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-McClain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • RobGRobG Member Posts: 1,850
    edited October 2013
    Did it ever work correcly?

    It looks like the piping to the manifolds is too small. You are not piped primary / secondary. That unit has an internal pump to handle the primary side. You are pumping into your expansion tank. I would suggest that you have all of your near boiler piping re-done per the instruction manual (which is very hard to follow). Get rid of the PEX for the primary loop and use the proper size copper or black iron. 

    Just my opinion. As well, you have no means of controlling the temperatures for the different zones.

    Only been installed for a week

    We've had the system for about a week now. Initially i thought the lukewarm baseboards were a result of the heating curve / outside temp sensor etc. Perhaps the boiler was just so efficient that it took into account the outside temperature was around 54F and didnt have to heat the water so hot to raise the temp in that zone. Then recently we had a really cold night at 32F and the baseboards still just seemed lukewarm. Thats when i got to looking in the manuals, watched the bosch install video online ( and noticed the primary/secondary piping they call out using a webstone closely-spaced tee manifold. Regarding the expansion tank, are you suggesting that it may be in the incorrect location? Thanks for the help!
  • gennadygennady Member Posts: 677

    Why are you acting as you want to troubleshoot your brand new installation? Where is an installer? And all this installation looks like nightmare on elm street movie.
    Gennady Tsakh

    Absolute Mechanical Co. Inc.
  • Aaron_in_MaineAaron_in_Maine Member Posts: 313

    That install is a joke. There is no primary/secondary piping. I would make him fix it.
    Aaron Hamilton Heating
    [email protected]
  • kcoppkcopp Member Posts: 2,746
    edited October 2013
    Not good....

    The plastic fittings are not rated for heat on the 1" pex. I have about 4 of these Greenstar boilers installed and that is not how to pipe them. I think you spent more time in the manual than the installer. Is this install in Vermont? FW Webb has plenty of training on these boilers.

    ....because I am concerned homeowner that is trying to understand and diagnose the problem. If i go back to the installer at this point and tell them that someone on a forum said that his work looks like nightmare on elm street, i don't think that will get me very far...
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    How to talk to the installer

    Just tell him what you told us-the system is not heating properly. Later on, you may want to show him this thread, but for the moment, just focus on the facts-you are cold! Part of the installation should be making sure the system functions as it should. Has he been paid in full yet (hopefully not).

    Since you have read the manual, his replies may be interesting and inventive! Bosch has a tech support line, and they may have something to say about the reversed tank location.--NBC
    tank location

    Thank you! The output was actually much better last night. I reviewed some of the settings in the FW200 control and it appears it was set to "radiator" instead of "baseboard" for heating. Changing it to "baseboard" seemed to make a difference, I was showing approx 170F water temp readings at the boiler after that (and the outside temp was around 40F).

    They have only been paid the 50% deposit so far so i have negotiation room. When you mention the reversed tank location, what exactly do you mean? I assume that you mean the expansion tank should be on the return side of the boiler? I noticed that all the line drawings in the Bosch application manual show the expansion tank on the return side.
  • nicholas bonham-carternicholas bonham-carter Member Posts: 6,535
    Talking to the installer

    Before he comes over to investigate the lack of heating, set all the controls back to where he left them.

    As he is looking at it, you can ask about the tank location, pipe sizes, etc. while you have the manual in hand.

    Others here may have other specific remarks about the installation--NBC
  • RobGRobG Member Posts: 1,850

    If you still have 50% of the contract you should first speak with the original installer and give him the option of making it right. If that does not work use the money for hiring a qualified installer to do it right.

    Does the PEX on any of the pipes say "for potable water only" ?

    Make sure that the slab gets some sort of mixing device. If you continue to put 170deg water through it you will destroy the slab and the piping in it.

  • IronmanIronman Member Posts: 3,406

    As others have pointed out, you boiler is not piped pri/sec which is required for a multi zone application like yours. See page 54 of the Applications Manual for the proper piping. The way it is now places the internal pump in series with the zone pumps which is improper.

    The left side hydronic connection on the boiler is the supply which means the circ's should be pumping away from the boiler. Check the directional arrow on the circ's to confirm this.

    The location of the expansion tank would be acceptable if the piping were pri/sec and the zone circ's were "pumping away" from it. The manual shows it in the return of the boiler loop. It is in the U.S. drawings and has been contended by more than one knowledgeable person as not being the correct place. Leave it where it is if the circ's are indeed pumping away from it. Just get it piped pri/sec as the manual shows. There's even an enlarged detail in the manual that shows how.

    The installer's workmanship looks well above average so I would conclude that he takes pride in his work and would want to correct his error. He just needs to get up to speed on his technical knowledge of that boiler. Apparently, he didn't realize it had an internal circ and the applications manual may not have come with the boiler unless Bosch has changed its practice.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • Aaron_in_MaineAaron_in_Maine Member Posts: 313
    edited October 2013
    This is right

    This is what it should look like the boiler drops straight into tees on the secondary loop.
    Aaron Hamilton Heating
    [email protected]

    Thank you very much for the comments. I appreciate your help, and everyone's help on this thread!

    Although the picture is pretty hard to see the piping due to size, I appreciate you taking the time to send it!
  • gennadygennady Member Posts: 677
    edited October 2013

    I do not want to sound negative, but workmanship here is not acceptable in my opinion.


    I do not see acid neutralizer on condensate drain line.

    I do not see BFP drip line extended to no more that 6" AFF

    I do not see min 18" before and after air scoop

    I do not see isolation and drain valve on expansion tank

    I do not see DHW mixing valve

    Just to name a few
    Gennady Tsakh

    Absolute Mechanical Co. Inc.
  • BobCBobC Member Posts: 4,406
    Click on that picture

    It will expand to a large size so it will be easy to see what is going on.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
    Zone heating when thermostat off?

    I'm thinking this new issue may be related to the lack of primary/secondary piping perhaps.

    I have noticed that when our two other zones are calling for heat and circulators pumping (rightmost two circulators in diagram) that the basement zone (circulator to the far left in diagram) is heating! The basement zone thermostat is off at this time and circulator not pumping but there is definitely hot water making its way through the zone/baseboards.
  • RobGRobG Member Posts: 1,850
    Basement Slab Heating

    This is happening because the pump inside the boiler is pushing past the zone pump due to the pumps being piped in series. What did your installer say about re-piping the boiler correctly?

This discussion has been closed.


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