Noritz Water Temperature Fluctuations

Discussion in 'Tankless Water Heater Forum' started by SDLtd, May 21, 2013.

  1. SDLtd

    SDLtd General Contracor

    Messages:
    3
    Location:
    British Columbia
    Our company is a general contracting and framing company and we built a spec home and sold it a year ago. We installed a tankless John Wood (Noritz) JWC111-DV NG hot water heater in the home. It worked fine until 3 months ago and since then our plumber has gone back maybe 8 times to fix it and is now stumped. The water temperature fluctuates from hot to warm and goes especially crazy when the toilet is flushed. This happens in all 3 showers and even in the laundry sink where the hot and cold inlets are separate. The John Wood customer service tech support thinks it is nothing to do with the tankless because I used a laser hand held temperature reader and pointed it at the outlet pipes of the unit and observed only a 4 degree F variation. One thing our plumber did discover is that the pressure from the main line and after the pressure reducing valve was coming into the house at over 90 PSI. He reset it to 70 PSI. This Noritz unit is supposed to be able to handle 150 PSI but do you think that this high intake pressure could have damaged the plumbing fixtures and their mixing valves? The plumber has flushed the lines (water is hard) and we believe we have eliminated the possibility of cross flow by turning off cold water to tankless and opening a hot water tap. Water flow stopped so all seals must be fine? Originally one of the toilets had a hot water line plumbed to it rather than cold but that was fixed a year ago. Anyway, do you think my handheld temperature machine would be reliable in this application? We will check the pressure after the PRV again. Please ideas would be appreciated. The homeowners are frustrated and our plumbers are out of ideas.
  2. Dana

    Dana In the trades

    Messages:
    3,027
    Location:
    01609
    First, to get any kind of accuracy with an infra-red thermometer you can't be looking at bare metal. Either paint the patch of plumbing with a flat black paint or wrap a short section with hockey tape and measure the temp of the tape, not bare pipe. (PEX is reasonably IR-emissive and need not be wrapped, copper/brass/bronze/galvanized is not.) You may still have a comparable delta-T, after giving it an emissive surface to read (or not) but at least you have a shot of taking good relative-temp measurements.

    There is a significant pressure drop across any tankless at high flow rates, and that only gets worse with time due to lime-up issues in hard water areas. As the pressure differences between the cold side and hot side get bigger, so to the interactions with anti-scald valves, but lime up can also affect temperature stability (particularly at low flow.) If you haven't already, descale the tankless (not just flushing the lines- it needs a mild-acid such as white vinegar to break down the scale, circulated for 15-30 minutes through the heat exchanger using a small pump. Don't forget to turn the power off to the unit while descaling lest you experience the joys of steam-driven jets of boiling hot vinegar spray.) In hard water areas descaling is often at LEAST an annual maintenance chore with tankless HW heaters, and often needs to be more frequent than that, depending hot water use and absolute water hardness levels. In these cases it's worth installing isolating ball valves on both sides of the tankless, along with ports for circulating a descaling solution through the tankless.

    The high static water pressure is not likely to be related to the problem.
  3. SDLtd

    SDLtd General Contracor

    Messages:
    3
    Location:
    British Columbia
    Hi Dana,
    Thanks for responding. I checked with our plumber and he did do a flush with vinegar. I did some asking around about the water and the hardness from that aquifer is 340 mm CACO3. Extremely hard. Manganese is 47 mg/L which is also really high. Not esthetically good for drinking water I guess. Anyway, my question now is whether a vinegar rinse would even be able to delime this degree of hardness?
  4. Dana

    Dana In the trades

    Messages:
    3,027
    Location:
    01609
    It's probably worth calling the Noritz help line and let them walk you through a debug:

    (866) 766-7489

    Or, get help via an online chat with a tech:

    http://www.noritz.com/home-owners/canada/ (see the pull-down menu under Technical Support on the upper left)

    The fluctuation may be a sensor going off spec or beginning to fail, if it otherwise has good flow and little to no lime scaling.

    Vinegar does a pretty good job if you run it long enough. If the thing has been in service for years it may take longer than a half-hour to get 'er done, but it'll still get there. Going at it with more aggressive acids might do it quicker, but do that only under the advisement of the manufacturer, who has a better handle on the alloy sensitivities of the heat exchanger(s).
  5. SDLtd

    SDLtd General Contracor

    Messages:
    3
    Location:
    British Columbia
    We have been working with the AO Smith/John Wood powered by Noritz help line for 2 months including several hours of trouble shooting between tech line and our plumber checking every possible thing that they could think of together. Thanks. The unit is just over one year old and worked fine for the first 8 months. I spoke with the city water quality people. Analysis of the water shows high iron and magnesium which are precipitating out when they add the hypochlorite. This is in addition to the high manganese and Calcium carbonate. I was just wondering if the iron and magnesium precipitates could be wreaking havoc. Oh my I really want this problem to go away! The city is aware of the all the struggles with water quality in this subdivision and are putting in new lines and hooking the area up to the main city water supply as of December this year. Meanwhile we struggle on.
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