Hot water reaches shower but not sink, why?

Discussion in 'Tankless Water Heater Forum' started by jinenjo, Apr 9, 2021.

  1. jinenjo

    jinenjo New Member

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    Hello. I am in a rental unit and it has a Takagi tankless heater. In the bathroom, the hot water never seems to reach the sink even if I turn on the hot water and run it for several minutes. I'm talking 5 minutes or more.

    The distance is relatively far, and the hot water takes a while to reach the shower, but it does get hot. I want to be able to shave in my bathroom sink, but it just doesn't work. The closest it's come to working is when I get out of the shower and turn on the sink. It is hot, but if I turn off the water and then turn it on again--nothing. And, when I try this method it still never gets as hot as the shower.

    Should I tell my landlord or is there a hack I can do here?
     
  2. Reach4

    Reach4 Well-Known Member

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    Maybe the threshold flow to turn on the WH is too high. See what happens if you unscrew the aerator, and open the hot faucet.
     
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  4. jinenjo

    jinenjo New Member

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    Thanks. I'll try that again. I think I already did and nothing changed.

    What if it does nothing?
     
  5. fitter30

    fitter30 Well-Known Member

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    What happens if you run the shower and sink at the same time?
     
  6. Reach4

    Reach4 Well-Known Member

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    I would try to measure the flow rate from the "hot" at the lavatory (time filling a container of known size).

    Then compare that to the minimum flow that should turn on the WH. Some tankless WHs have a setting to adjust the minimum activation flow required.
     
  7. jinenjo

    jinenjo New Member

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    Great ideas. I'll try them all out and report back in a few days.
    Thanks
     
  8. jinenjo

    jinenjo New Member

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    So, I haven't done a complete battery of tests, but I think I know the culprit.
    To test the flow rate for hot water, I used the sink in the kitchen (which is very close to the WH, right outside on the other side of the wall). I turned the kitchen sink to hot, but at a flow rate similar to the bathroom and it never became hot.
    Then in checking back on the bathroom, I realized the bidet tube may be diverting water pressure from the valve because it's turned all the way out and the flow is still low.
    So I either need to change the flow setting on the WH (if it's even adjustable--it seems like an older unit) or move the bidet tube to the cold water side.
    I'm not experienced in plumbing, hot water heaters or anything, but I am handy and can follow instructions well.
    bidet.jpg inside WH.jpg outside WH.jpg
     
    Last edited: Apr 12, 2021
  9. Reach4

    Reach4 Well-Known Member

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    That is a good test. Try that one without the aerator.
    It's not that. If your bidet attachment has a connection to the hot, it probably also has a connection to the cold, which may tee off a the toilet tank). But the presence of the tee to the bidet attachment is not going to be the problem.

    You want to identify your WH, and see if you can get a manual with specifications and possible settings.
     
  10. jinenjo

    jinenjo New Member

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    I ran the hot water faucet in my bathroom without the aerator and nothing happened even after 3 minutes.

    Then I turned on the shower and it did indeed get hot water flowing to the sink.

    I looked up the manual. The model is TK-2, apparently from 2006.
    This is what it says: "0.75 gallons per minute is required to turn the burners on;, after the burners are ignited, the flow rate can be lowered to 0.6 gallons per minute to maintain the heater on." There does not appear to be an option to adjust the rate at which it's ignited.

    I tested the flow rate of the bathroom sink without the aerator and its .5 gallons per minute. It took 2 minutes to fill a gallon jug.

    Are you sure the tee is not the issue? There is only one tee going to the bidet, from the hot water valve. If that's not it, how can I increase the flow to the sink? the valve is opened up as far as it can go.

    THANK YOU BOTH FOR ALL YOUR HELP SO FAR!
     
  11. Reach4

    Reach4 Well-Known Member

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    Not totally sure, but I doubt it.

    At this point the question for me is "why is the flow to the lavatory and kitchen hot less than 1 gpm?" As a test, turn on your bathroom faucet to all cold. Does water come out faster then? No such tee in the cold line. How about setting the control to the middle (hot+cold). Does flow increase much? I understand that the cold flow does not contribute to the WH coming on.

    Limed up piping? Partially closed valve?
     
  12. jinenjo

    jinenjo New Member

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    You're probably right. The bidet tee is not the problem.

    Just to clarify, the bathroom hot water is .5 GPM, but the kitchen is much faster. I didn't measure/time it (just judging by sight).

    The cold comes out much faster in the bathroom compared to hot. When I set the control to the middle it's slightly more than the cold by itself.

    I understand what limed piping is, but what could be a partially closed valve? Where? The valve under the bath sink is fully opened.
     
  13. fitter30

    fitter30 Well-Known Member

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    New bathroom faucets have a flow.rate of 1.5 gpm
     
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  14. Reach4

    Reach4 Well-Known Member

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    I think replacing that valve on the hot seems worth trying.

    If that is a compression connection, something like this seems good:
    [​IMG][​IMG]
    There are lots of variations. The second output could be 3/8 OD or 1/4 OD, which yours may be. I don't know if you would need to replace the nut and ferrule, or if you could leave that. Or maybe your valve is on a 1/2 inch nipple, and you would unscrew that and screw on a new valve. Depends. I suspect the valve is compression.

    Is the problem the valve? I don't know. That may be the most likely, but not sure.

    How do you measure the flow out of your faucet? There are various methods. One is to put a container under there, and run the water for 30 seconds. Then measure how much water got collected. You can measure water with measuring cups, or you can use your kitchen scale to weigh the weight change.

    One more thing: if you have a pressure reducing valve, you may be able to turn up the water pressure to get increased flow through your existing valves. If you adjust the PRV to a different pressure, you would also want to adjust the air precharge for the thermal expansion tank.

    I think a plumber could probably get your flows sufficient with one trip if you described the problem as the lavatory and kitchen flows being too low to be detected by the tankless WH.
     
    Last edited: Apr 14, 2021
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  15. jinenjo

    jinenjo New Member

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    The bath sink seems like a modern faucet. Well, at most 10 years old or less.

    I'll look into replacing the valve.

    I measured the water flow by filling up a gallon jug and timing it. You may've misunderstood, the kitchen flow is strong. The only problem is the bathroom sink.

    Where would I find the PRV if there was one?
     
  16. Reach4

    Reach4 Well-Known Member

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    I had read this statement:
    I now suspect that you meant that when you turned the kitchen sink hot on at a slow rate, the WH did not cut on, but if you fully opened the faucet in the kitchen, the WH did come on.
     
  17. fitter30

    fitter30 Well-Known Member

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    Retired service tech
    Location:
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    Lets see at what gpm the heater turns on. Kitchen sink measure flow and adjust faucet to .5 did the heater come on
    No adjust to .75 till heater comes on. Measure flow in bathroom see where your at. Pull aerator still no hot water replace shut off valve and check for scale in piping.
     
  18. jinenjo

    jinenjo New Member

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    Apr 9, 2021
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    San Francisco
    That's correct.
    I will try and replace the shut off valve. How would I check for "scale" in the piping?
    Can I use an auger to clean it out? I recently purchased one to clean hair out that clogged the bathroom sink and shower.
    Thanks again for both of your inputs!
     
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