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Flow direction - baseboard heating

dpenny
dpenny Member Posts: 8
in Gas Heating

I have a 12 yr old Rinnai tankless used for baseboard heating ONLY. Mild climate, 2 weeks of 25F weather. Did not work well this season. Am having hard time getting anyone to come to service it or replace.

So, I am first trying to understand what I have. Plse see attached diagram. How do I figure the flow direction in the ONE pipe? And is pump placed correctly?

_Rinnai Piping.pdf

Comments

  • jesmed1
    jesmed1 Member Posts: 1,073
    edited March 1

    Can you post some photos of the boiler and associated piping? The diagram doesn't make much sense.

    You said the system is 12 years old. Did it ever work right?

    mattmia2GroundUp
  • dpenny
    dpenny Member Posts: 8

    I've been here 6 yrs, and it seemed OK. We must have had colder seasons than this one.

    Photo attached. Hope it + my drawing make sense now.

    Rinnai1.JPG
  • jesmed1
    jesmed1 Member Posts: 1,073
    edited 12:35AM

    @dpenny Here's my attempt to understand your photo.

    We need to know where every supply branch goes and every return branch comes from, because without a full piping diagram it's impossible to know what all the possible flow paths are and which way the water "wants" to go.

    1. Just before the pump, there's a tee where a return is coming from above, and another return is coming from under the slab. Where is the upper return coming from?
    2. Just before the Rinnai, there's a tee where a return is coming from above, and the other return is coming from under the slab. Where us the upper return coming from?
    3. The supply main goes off to the left out of frame, beyond the expansion tank. Where does it go?
    4. The supply seems to branch off somewhere out of frame, then it reappears coming down the wall to the left of the Rinnai. Where is it coming from?
    5. The supply seems to branch off into a tee at lower left, going horizontally out of frame, before it goes down into the slab. Where is that supply branch going?
    6. If there is only one supply going down into the slab, why are there two returns coming out of the slab? You have to show all the piping and radiators "below the slab," otherwise there's no way to know what the likely pressure differentials are between those two returns.
    7. Is there a circulator built into the Rinnai?
    8. What controls the Grundfos circulator? Does it always run when the Rinnai is running, or are there some times when the Rinnai is running but the Grundfos is not?
    9. Are there any other circulators not shown?
    10. I don't see any air eliminators. Are there any?
    Rinnai with arrows.jpg
  • dpenny
    dpenny Member Posts: 8

    1st… THX for your detailed thoughts and annotations to my photo. My eariler "drawing" showed the key point/parts. The key point and Q is #6. Regardless of deltaPs below slab, the highest pressure is right after circulator, so therefore I think the flow is down into slab, with H2O at recirc temp, not Rinnai hot output temp. I am thinking the circulator is mis-place and has been for 12 yrs.

    7. there is no circulator in Rinnai

    8. Control: single theromostat (on/off) controls circulator thru AC relay. Flow turns on the Rinnai cuz it is a tankless domestic water heater.

    10. there is one air eliminator to left of pressure vessel, and one way above your label "upper return" which is not a return, but air eliminator up in attic.

  • psb75
    psb75 Member Posts: 1,004

    You are not providing adequate representation of this installation. The photo and your drawings are woefully inadequate for a proper diagnostic by those of us on the forum. Provide some more anecdotal operational history of this installation as well. It should be stated right off the bat that this Rinnai on-demand water heater is the wrong machine for this purpose. Has it ever been flushed? There don't seem to be any temperature or pressure gauges. Provide an electrical (control) schematic of the installation. How big is the slab (sq.ft)?

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