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Slant Fin Liberty L-30 Tankless -- Hot water goes luke warm!

Constantin Member Posts: 3,796
... rather I believe your issue is related to the lack of a tempering valve after the coil. I'd have a plumber retrofit a mixing valve to temper the water coming out of the boiler down to a safer temperature (i.e. below 120°F).

Not only will a quality valve prevent you from being scalded, it'll also hopefully put an end to the pulsing/hunting behavior that you have noted temperature-wise.

If that doesn't solve it, I'd recommend a indirect water heater to be piped off the boiler as a priority zone instead of using the coil. A coil can't usually take advantage of a boiler the way a indirect water heater can due to the different sizes of the HX. You'd also want a mixing valve on this kind of a rig.

Call a plumber or a hydronic heating professional, they ought to know what you're talking about and how to fix it.


  • C Foote
    C Foote Member Posts: 2

    Hi Guys,

    I hear there are some Slant Fin experts on this board so I thought I would see if someone can point me in the right direcion with my problem, or at least who I should direct my question to -- a furance expert or a plumber?

    I have a Slant Fin Libery LD-30 with a tankless coil. The unit is 12 years old. The coil was replaced 3 years ago in 2003, it has a 4.5GPM flow rate. The original apparently broke.

    The issue is this -- when taking a shower, initially I get hot water for about 45 seconds, but then it jumps to luke warm. It stays luke warm for about 30 seconds, then it gradually kicks back in and can get really hot! Then after a minute or two it goes luke warm again and gets really cold. It's driving me nuts as you can imagine.

    The Aquastat was originally at 160 low, 180 high. I adjusted it down to 145 low, 165 high because I was getting scalded in the shower when the temperature was changing. It didn't help the problem at all, but at least now I'm not getting burned.

    I think part of my issue is that my valve in the shower is 40 years old and does not have any temperature control features built in, but this is happening on ALL of my plumbing fixtures (faucets, other showers, etc.)

    Any thoughts on what the scoop is with this? Bad mixing valve? Bad coil? I just bought the house, and the lady was good about having a tune up every year. I am the only person living in the house, so I'd like to try and stay away from getting a hot water tank.

    I have a feeling it could be a sensor of sorts (the boiler is not kicking in soon enough to heat the water?) that is becoming lazy -- are these sensors replaceable?

    Any advice is welcome. I had a 2 year old Weil-McLain tankless unit at my previous house and it never gave me any problems at all. I don't sit in the shower for an hour -- I'm in an out in about 5 minutes.

    Any advice is appreciated!


  • jackchips_2
    jackchips_2 Member Posts: 1,338
    Not many

    can say it well as Constantin. Good advice based on the description given although it's possible you have a mixing valve and it has gone bad.

  • Constantin
    Constantin Member Posts: 3,796
    Very good point...

    ... there may be an extant valve that is malfunctioning. Either way, I'd address the issue at the source so that all fixtures in the home are protected. Thanks for the kind words, Jack.
  • Rudy
    Rudy Member Posts: 482

    Thank you guys very much for the information! You don't know how much of a sigh of relief it is to hear that its not something major.

    Just to make sure I don't appear to having a mixing valve (I can't find one in the piping, but maybe you guys can?), here are some pictures of the piping. Let me know if you need a close-up picture of anything and I'll be happy to oblige.

    Just copy and paste the link into your browser.



    Thanks again for your time and help.

  • Nick L. in Vt
    Nick L. in Vt Member Posts: 87
    mixing valve

    valve is a watts 70a, has hot/cold/mix imprinted on it. we usually pipe ours below coil as in the mnfctr drawings.
  • I had the same exact problem

    You get in the shower and have hot water for a minute or 2 , then it goes lukewarm , then after another minute or 2 it goes back to hot .

    What I had was a similar oil boiler with a coil and aquastat like yours , set at 180 hi and 150 low , with the diff setting high . On the mornings where there was no call for heat , the boiler temp would be too low to sustain a good shower until the boiler came back on . Boy did the family hate messin' with the shower handle every minute .

    Initially I changed the settings to 190 hi , 170 low and the diff as low as it can go . It worked better , but nowhere as good as converting it over to an indirect tank , which I did a few months ago . I would try upping the settings on the aquastat first and changing the guts in the mixing valve . If the problems still persists , a storage tank is a relatively inexpensive option for steady hot water at the showers and sinks . But .... an indirect tank is the best option , in my opinion .
  • mario & luigi
    mario & luigi Member Posts: 11

    a stainless steal indirect is the way to go but if you don't have the money (since you just bought the house) you can get a tank and a thermosat with a pump tha will store water using your coil to heat it 30,40, or 70 gallons. Superstore and Everhot make these devices. They usually come in a little less than half what an indrect costs
  • Weezbo
    Weezbo Member Posts: 6,232
    It has the sound of a bad mixer....

    an old way to get some mileage out of a coil is to run the cold water into the coil, come out of it to a water heater, on its cold side run the hot into a mixer then run the mix into the buildings supply.

    an "up grade on that is to put a T on the drain bring a line up from it put a bronze body pump on it, send it back into the cold into the coil with a check on the cold side....run it off the upper control of the water heater...

    a further up grade it to connect a recirc system into this lash up, it allows you to have 90 degree water at the tap in seconds... if you so choose, you may elect to wire the elements up to function during the time of the year that you may not need the boiler running....or in conjunction with the boiler for faster recovery.... next step up is a heat exchanger tapped off the cold water into the water heater to the coil.... after that is an indirect :) dont worry , insist on an anti scald devise on your next lash up :)ans a S-T 12 :)
  • jrc2905
    jrc2905 Member Posts: 98

    You need to hire a plumber, everything on your hot water side is piped wrong. Not a big job but needs to be repiped.
  • C Foote
    C Foote Member Posts: 2

    jrc2905, thanks for the info. Can you elaborate a little bit more? I want to make sure the next plumber coming over does this right, so have the info (even if I don't understand it!) on doing it right would be very very helpful.

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