Stiebel Eltron Tempra 29 Plus, issue with shower

Discussion in 'Tankless Water Heater Forum' started by Atticweb, Dec 7, 2013.

  1. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Hope I have the right place, I'm new here.
    Just had installed the electric tankless model in title of this post, and upgraded my electrical supply to 200 amp to handle it. Costly but various reasons for doing so (venting issues, etc.).
    All work was well done. Everything works fairly well, minus wait times for hot water and occasional cold shots when someone else turns on a faucet.
    Main issue follows with the pertinent facts; I've seen other similar issues here with showers, but I believe mine may be different.
    Facts are this: one shower and one sink in one bathroom, upstairs, both off the same hot water supply line.
    Sink is within couple degrees of set temp on unit (set to 108° for example, get at least 106°).
    Shower, the supply for which breaks off same pipe as sink, is 20° colder! Luke warm at best.
    The SE unit adjusts pressure to the temp requested; that is, to keep desired temp, it reduces gpm.
    I have an old Moen shower faucet/mixer type, over 30 years. I'm pretty sure it must be mixing cold with the hot and basically not "talking to" my new tankless. I don't think the cartridge has anti-scald it's so old, but it might. Seems to me if you can set your heat at the unit, you don't need the anti-scald. Also the "posi-temp" feature seems like it might interfere with what the tankless is attempting to regulate.
    I've found no help online or anywhere else so far.
    I was all set to order a two-valve non-mixing Kohler unit to replace the mixer, as I'd like to be able to control just hot, etc., myself without the mixer deciding what's best for me and fighting with the heater.
    To keep already high expenses down, a plumber just convinced me to just replace the cartridge and thinks that might do it.
    Any thoughts or suggestions would be helpful, and also any discussion of these mixer features vs. tankless flow control and temp setting may be helpful for others.
    Thanks for your time.
    Will James
  2. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Something I forgot to mention. I left the old tank for now, just put shutoffs on both the cold and hot lines to it. Swapped out the tankless for the tank this morning to get a hot shower. No problem. So, don't see how it could be the mixer (shower faucet) if not affected when going back to the tank. This is one for Sherlock seems to me. Help?
  3. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,819
    Location:
    New England
    Does your shower have an old showerhead or one of the newer, flow-restricted ones. An old one may just try to flow way too much volume, and the tankless can't keep up. Also, if it is a single-handle valve, it may have a limit cam/screw/lock and that is preventing it from going to all hot. Buffalo can have some very cold inlet cold water temperatures...what does yours measure? For most people, an electric tankless, except as a single point of use item, is usually inadequate, as their flow rate is way too small for some uses.
  4. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Thanks for the reply jadnashua. Removed limit cam, no better. Yes the inlet water is cold, I live in Buffalo, but I researched this thoroughly before buying and it works great including unrestricted high flow in basement tub. Does slow up a bit sometimes to keep temp requested. I realize I can't raise temp to 120° and get great flow, just not a 20° drop from same hot water supply at reasonable level. Went with the 29+ instead of 24+ which was ok for this region to get the three heating modules. I'm not expecting perfection, but it's made to handle this temp increase (50° to 110° e.g., 60° rise). Can't keep my hand under the sink hot only a few feet away. Think if I could swap out the old Moen standard single with same (may be letting cold in, very old), might do it; but posi-temp and balanced control is going to mess with the unit which modulates and sets high temp itself. Hope that made sense. Thanks again, see what I can do!
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,819
    Location:
    New England
    FWIW, I've measured incoming water temp here in southern NH at 33-degrees, so if it's capable of 60-degree rise at full flow, that's not even body temp. Most single handle shower valves don't have a means to adjust the flow rate, so it's trying max all the time. Once you direct it to the shower, that has some flow restriction (if it is a recent head, otherwise, who knows). A vanity faucet is typically restricted to about the same as a showerhead (if not lower). Could be an issue with that valve...just don't know enough about the inner workings.
  6. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Incoming is 50° now. I just don't see a 20°drop from the sink same supply a few feet away. Was thinking about putting in Kohler two single valves (just turn cold off) but plumbers don't seem to want to install it.
    Also if shower is restricted (I'm getting same results tub/shower), wouldn't it bring it down to about the sink and I should get same temp?
    Might be of interest: http://www.tanklesswaterheatersdire...rheaters/stiebeleltron/stiebeleltronspecs.htm
    Last edited: Dec 9, 2013
  7. Dana

    Dana In the trades

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    The pressure drop at full flow across a tankless is substantial even when it ISN'T restricting to maintain temp, and which can interact with shower mixers.
  8. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Which is why I'm thinking about swapping out the mixer with something like this that I can control.
    KohlerJob.jpg

    Also... doesn't take me long ;) - finally went downstairs and shut off the cold water supply. Bingo, immediate hot water from tub (tankless). It's the mixer.
    Last edited: Dec 9, 2013
  9. lifespeed

    lifespeed Member

    Messages:
    320
    Location:
    California
    I have not encountered any issues using a thermostatic shower valve and a tankless (natural gas) water heater. The mixer adjusts the balance between hot and cold. Yes, the tankless sees flow variations but they can deal with this.

    If your mixer does not allow you to close the cold supply nearly shut this would, of course, cool the temperature. It is not clear to me that a "dumb" mixer is required to fix your problem. Perhaps just one that isn't "broken" or a flawed design that can't close the cold side.
  10. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Thanks for that info lifespeed. So you're saying that if a mixer is working properly, and you turn it all the way to hot, there is absolutely no cold mixing in? I thought I read that such valves need both hot an cold "pressure" to work. Please clarify, thanks much.
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,819
    Location:
    New England
    The spool valve closes when the incoming supplies are not equal, it isn't about what is actually flowing, it's the available pressure. So, if you have small lines, and someone say flushes the toilet, the cold water pressure drops, and the spool valve moves to reduce the hot going out, trying to maintain the balance. So, it's pressure, not flow (unless it gets extreme to a trickle) that those valves work on. If the plumbing was ever done with a permit and inspection, it would not pass if it did not have an anti-scald valve newly installed. The fact you can buy them does not mean it can legally be installed for a shower (maybe for a tub only).
  12. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Is that nationwide or local?
    I do not want the spool valve to do this: "reduce the hot going out" under any conditions. Again, I control that at the tank. Anti-scald is accomplished at the unit; I have it set to 210 right now and the cold shut off. Loses a few in cold pipes and comes out adequately hot (not extreme as the unit would reduce my flow to keep temp as requested at unit). Ergo, no possibility of "scalding" anything at any time. This code must have been written without considering this tech. It seems as though everyone is talking gas models (wherever I go inc local plumbers), not electric, and don't seem to be familiar/experienced with Stiebel Eltron whole-house units. Thanks for any more thoughts going forward. Now that I've shut off the cold completely to upstairs (which is slightly annoying), I can set the temp of my shower exactly so I've just gained a bit of time, still have to decide on the course of action.

    As far as the term "dumb" valve that I propose purchasing and installing (several are available, looking at paying more for Kohler for quality and because I'm from Milwaukee), I prefer the valve to be "dumb" and me to be "smart" instead of the valve being "smart"... think I'm already clear on that. As someone posted elsewhere, I learned early how to turn the knobs and mix the water. Thanks for all responses.
    Last edited: Dec 10, 2013
  13. lifespeed

    lifespeed Member

    Messages:
    320
    Location:
    California
    So, you're having a problem with an old, broken, bad-design or scaled-up valve that won't shut down the cold. Then you predict that new pressure-balanced and/or thermostatic valves are going to have a design flaw where they can't shut down the cold water? In your application the thermostatic is likely more appropriate than the pressure balanced. Lacking evidence to the contrary I don't share your conviction that the only valve that will work is 20 year old tech.

    Perhaps this evening I'll turn the temperature down on my tankless to 105F and see if my Toto thermostatic shower valve maintains the 104F setpoint . . .
  14. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    I'm not predicting anything. Just going by what I read, which is often contradictory and/or irrelevant to my situation. Why do you recommend the thermostatic? This is the kind of suggestion with fact I'm looking for. Valve looks a bit pricey. I see you're in California, pretty sure you won't have an issue with temp rise at full flow.
    Last edited: Dec 10, 2013
  15. lifespeed

    lifespeed Member

    Messages:
    320
    Location:
    California
    Thermostatic because it does not reduce pressure to accomplish "pressure balanced" when one side of two inlets experiences a pressure drop. Pressure-balanced are the cheaper and original anti-scald. Thermostatic are much nicer to use with set-and-forget behavior.

    California warm water vs NY cold water, electric vs natural gas, in the end none of this really matters with regard to your valve. At the end of the day you need a valve that can put out, say, 105 degree water with only 108 coming in the hot side so it's range must include full hot.

    Yes, the Toto valve is expensive but does work really well. There are other options (Grohe for example), although I don't know if they're much cheaper. Toto replacement cartridges are inexpensive, which is NOT the case for many of the products you'll find at Home Cheapo.

    I'll try the experiment I mentioned as it is really easy, and confirm whether or not the Toto valve can operate as desired.

    Edit: I know thermostatic valves are required to be capable of completely shutting off the hot water if cold pressure is lost entirely (safety). The question is: can they do the same in the opposite direction?
    Last edited: Dec 10, 2013
  16. Dana

    Dana In the trades

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    2,785
    Location:
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    Especially with a GAS FIRED tankless, which is less flow restrictive (= less of a pressure delta between the hot & cold sides at the mixer) and has much higher BTU/hr output.

    Not that it's going to help this situation, but an electric tankless will be marginal at mid-winter incoming water temps in Buffalo, even after you've fixed the mixer balance problem. The Tempra 29 is going to be pretty much maxed-out at normal shower flows at the end of January when incoming water temps drop under 40F. The deep subsoil temps in Buffalo are under 50F, so as we go into the real winter it doesn't take long for the water temps to drop- it's not much in the way of passive geothermal heating from below. You could perhaps buy more showering capacity with a drainwater heat exchanger, but that wouldn't help batch draws (like tub fills) a bit. With the Tempra 29 you'll have to schedule other hot water use for when nobody is using the shower, at least in the winter. For a 1 person household it's not too tough to manage, but for a 3-4 person household it's a bit of a pain. (Been there, done that.) That would not be the case with a 199KBTU/hr gas-fired tankless.

    The IPC hasn't allowed either the temperature control on the water heater, the temperature controls at the shower mixer, or the anti-scald at the mixer as acceptable alternates to pre-tempered water distribution at least since 2006, and probably before then. Anti-scald valves on showers is still explicitly required, even with the tempered water distribution. (See section 607 of IPC 2012 )Routing untempered water to dish and laundry is allowed, but not to bathing/lavatory. Most people with tanks put the tempering valve at the tank, and only distribute tempered water in their hot water plumbing. State wide NY is still under IPC 2006, but some municipalities may have upgraded. You'll note the verbiage regarding tempered water distribution and anti-scald valves hasn't changed much.
  17. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Thanks, I've been reading about the thermostatic and still don't get it. The fact is my Stiebel Eltron Tempura 29 Plus *controls* and delivers the exact water temp it is digitally set to, by reducing flow if necessary. So, purchasing a valve whose main attribute is to do that also not only doesn't make sense to me, it seems, like I've said before, that it would possibly interfere with the pressure balancing and temp control that is inherent to the way the SE unit works. Again not predicting that, just trying to make sense of it all to choose the best option for an electric tankless that is built to always deliver the same temperature, always adjusting it for incoming and other factors.
  18. Atticweb

    Atticweb New Member

    Messages:
    12
    Location:
    Buffalo, NY
    Thanks Dana, your post came in while I was replying to another. I used the temp rise charts from SE and an independent source to choose the 29 Plus (some saying I was borderline 24+ but I went for more), realizing that probably no other use while a shower is taken would be SOP. That's no problem for us empty nesters; venting a gas unit is (for various reasons in this 160-yr-old house) not an option. Thanks for the code I'll have a look at, very helpful. I assume it was written before units such as mine that make it impossible to scald oneself. You seem very knowledgeable; adhering to code and understanding my situation, which valve replacement type would you recommend and why? Even brand if you don't mind.
  19. lifespeed

    lifespeed Member

    Messages:
    320
    Location:
    California
    Most people have an expectation of being able to adjust the temperature inside the shower rather than walking to the water heater control panel, although in your situation you will face an upper limit imposed by your water heater and other factors. I have not seen the issue with water heater temperature control and thermostatic or PB valve interaction you are theorizing. Really, this is a basic water heater design requirement. An inability to maintain temperature over a range of flow rates would be a failed design. I doubt you will see this, I know I don't in my setup. You could test with a thermometer while you varied the flow at a hot tap. Should stay fairly constant.

    Edit: down the road as incoming water temps change you may like the option of setting your water temp to 110F or higher for various reasons. A thermostatic valve makes the shower temp constant regardless of hot water temperature (so long as the minimum input temp is met).
    Last edited: Dec 10, 2013
  20. Dana

    Dana In the trades

    Messages:
    2,785
    Location:
    01609
    Electric tankless water heaters and others with precise settable temps existed long before IPC 2006 was drafted. Having a thermo-mechanical tempering valves are designed to protect even when there is a fault condition in the hot water heater or the water heater is cranked way up, and anti-scald valves are designed to protect when there are large or sudden pressure differences between hot & cold. It's the anti-scald features that interacts with the high pressure drop of an electric tankless at full flow.

    Even though I understand the nature of the problem, I don't have sufficient familiarity with the array of mixers & electric tankless units out there to make a particular recommendation on the mixer here.

    There are any number of thermostatic mixing valves that could be put on the output of the Tempra 29 to make it code-compliant, and if you crank up the temp on the heater, then dial it back down with the valve, you would have somewhat less pressure difference between cold/hot at the mixer.

    In much of the world the electric water heater for showers is at the shower head, and there are no separate hot/cold feeds, but that isn't the US standard.

    Were this day-1, before up upgraded the power and installation of the electric tankless I might have recommended going with a tank type electric hot water heater (or maybe a hybrid heat-pump version if sufficiently subsidized in your neighborhood.) Tankless hot water heaters have these issues, and sometimes it's just not worth the aggravation, but the reasons for going tankless vary. Space savings is one common theme, never running out of hot water is another, then somewhere down the list the higher efficiency aspects are real (if pretty small with electric tankless). But electric tankless hot water heaters work better in locations with warmer incoming water temps than in the cool northeastern US.
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