Understanding my tankless with recirc system

Discussion in 'Tankless Water Heater Forum' started by AaronHartwell, Mar 22, 2012.

  1. jastori

    jastori New Member

    Messages:
    118
    Location:
    Illinois
    Are you sure that the pump is not pumping to the right in the picture? Your "??? Water" pipe would typically be the return of the recirculating loop.
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Look for a direction of flow arrow on the pump.
  3. AaronHartwell

    AaronHartwell New Member

    Messages:
    10
    Location:
    Duvall, Wa.
    Ewww… Good question. That would make more sense if the pump was pushing water to the right. It seems like that green valve (barely visible behind the yellow gas line in the photo) would need to be closed if that's the case.

    I'll check the pump tonight to see if it has any markings.
  4. AaronHartwell

    AaronHartwell New Member

    Messages:
    10
    Location:
    Duvall, Wa.
    Ok, so there's an arrow on the back of the pump that would indicate the pump is indeed pumping left to right. So the ??? line is in fact the hot water return.

    Now I'm curious about the green valve. I wonder if that's cold water coming in with a one-way valve.
  5. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Looks to me your check valve is in the wrong location. It should be located just after the stop valve at the wall on the cold side. The direction of flow would be toward the heater.
  6. AaronHartwell

    AaronHartwell New Member

    Messages:
    10
    Location:
    Duvall, Wa.
    Ok, so I just took the cover off the Takagi TK-3 water heater and pushed a button that's supposed to bring up any error codes. I threw a 3-2-1 code which maps to "Inlet Thermistor Fail" Assuming the inlet and outlet thermistors work together to control temperature and decide when to power the pump, having a bad one on the inlet seems like something that could cause the water to randomly go from hot to cold.

    I've searched on the web and can't find parts for this thing. Where would I go about getting a replacement thermistor?

    As for the check valves, I'll look at that Hackney. Given that things worked well for a long time and suddenly started failing I'm guessing something has gone bad vs. things are plumbed wrong but as I said in my original post, it wouldn't surprise me if things actually are plumbed incorrectly given the sub. :)

    Aaron
  7. jastori

    jastori New Member

    Messages:
    118
    Location:
    Illinois
    If I'm understanding correctly, the green valve is the supply of cold water to the heater. If you close that valve, you will have no hot water at all ! Keep in mind that the recirculating loop is important only when hot water is not being used - it keeps the water in the pipes hot for when needed. Once you start using hot water, the recirculating loop has very little effect on the system - then you need cold supply flowing through the heater to create the hot water.
    Last edited: Mar 27, 2012
  8. AaronHartwell

    AaronHartwell New Member

    Messages:
    10
    Location:
    Duvall, Wa.
    Jastori - Thanks for the clarification. That makes sense and is consistent with what I decided last night after looking at the system a bit more.

    I'm pretty convinced the error code I mentioned above about a bad inlet thermistor is the culprit. Now I just need to figure out where one gets a thermistor for a Takagi TK-3. Anyone know?
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,820
    Location:
    New England
    While a thermistor might fail, they're pretty robust SS devices...it might be the control board. Often, there's an easy test for a thermistor if you have a multimeter...the resistance at a specific temperature can easily be read. A pot with some water in it and maybe some ice, and you can check that it changes over temperature changes according to the spec sheet (which might be in the manual).

    As said earlier, some tankless systems/models void the warranty if you add recirculation, or don't do it per the instructions. Regardless, it does stress the thing more than without, at least in a typical home. Another reason why a commercial installation and residential tend to have different length warranties.
  10. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Sell it all on ebaby and get a nice electric water heater without any circuit boards.

    And what Jad said: you get super hot spots on shut down and pauses in circ. - thats why they crud up so quick and you get a 30% efficient unit fast.
  11. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    On the western slope of the Cascades they don't crud up very quick at all- take that one off the checklist. ballvalve's "bottled water quality"== added minerals for fresh taste.

    And if you run it at 110F instead of 140F, even in bottled-water country it can go decades without appreciable loss of performance, but not in TX. 140F would be a tank heater reference point, and you'll rarely need more than 110-112F out of the tap, so when it doubt, turn it down.

    SFAIK recirc doesn't void the warranty on the TK3 as long as it meets their minimum pump sizing specs. (Scoll down to the discussion near the bottom of the page.)
  12. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,820
    Location:
    New England
    The only thing in a typical home that needs fairly hot water is the dishwasher. But, at least some of them can heat their own water if the incoming water isn't hot enough. Without one or the other, the DW will not perform very well. same is true with a washing machine...many stains and things can be removed with cold water. But, should you need hot, some of them can heat the water, or will require greater than the nominal 110-degree water that may be fine for bathing. So, it really depends on what your needs and desires are.
  13. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    No matter the water, life cycle testing shows the flow thru's to be a poor economic and maintenance choice.
  14. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    True-dat.

    But since it's already installed and working-mostly, fixing minor issues like this and getting the full lifecycle out of it is a better choice than just scrapping it (at least most of the time.) He's asking how to deal with it, not whether it makes sense to install one. TK3s will hang in there for a good long time in naturally-soft water country with fairly minimal maintenance, even if there's no "payback" in a financial sense on the somewhat higher efficiency.
  15. AaronHartwell

    AaronHartwell New Member

    Messages:
    10
    Location:
    Duvall, Wa.
    Yep, that's my thinking as well. When it's shot, I'll pull it and go with a tank.
  16. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    If you have hydronic (pumped hot water heat), you'd be better off with an indirect tank running as special heating zone off the boiler than with a standalone gas-fired tank.

    Unless lighting strikes and fries all of the controls on the TK-3 it could literally be decades before it's not worth fixing anymore though. They're neither as bad as the detractors make them out to be (or as great as their proponents.) Condensing tank hot water heaters can be pretty reliable- they're not nearly as complex under the hood.
  17. bethy1116

    bethy1116 New Member

    Messages:
    1
    Location:
    New York
    Hi all,

    I'm hoping you can help us. We just had our well replaced and are having problems with our tankless hot water heater. My husband has flushed it several times as we we clearing sediment from the lines. The first time he flushed it with vinegar, everything seemed fine. We were having problems with hot water pressure dropping throughout the house and he thought he would flush it again. He has had a hard time getting the heater to flush properly with the flow being restricted even during the flush. Any suggestions?
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