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wiring issue w/ triangle tube indirect & buderus boiler?...

hey there. i just bought a triangle tube smart50 to use with my buderus gb142 (which i've had for about 2 years now). my plumber installed it, it looks good, but he advised me that he's nervous of wiring/electrical devices he doesn't know much about. i'm alright at wiring electrical devices, so i figured i'd give it a shot. that said, i've spent the past couple days troubleshooting why i didn't have hot water in my taps. here's my situation...

on my buderus, there's a number of low-voltage 2-wire molex-style connector slots. one of which is for the temperature sensor from an dhw heater. after much trial and error, i figured out that the only dhw sensor that seems to work with my buderus is the one that came included with it; not any others (like the jumper i made to go from the smart50 to the gb142).

i powered down the system, and as soon as i plugged in the stock dhw buderus sensor, it activated the dhw side of the boiler the next time i fired it up. however, as you could imagine, the hot water section kept cycling and cycling, as the sensor was only picking up ambient air temperature, and no matter how much hot water was pumped through the indirect, the temp sensor never budged. obviously. so i turned the boiler off when it started to really heat the indirect's water.

so, in trying to figure out where to stick this sensor (apart from directly attaching it to the return line to the boiler), i decided i would just replace the stock triangle tube dry well sensor with the buderus one...seeing as how that seems like the only way to activate the buderus dhw section.

here's my issue(s): the metal sensor portion of the gb142 was nearly identical in size to the stock sensor on the smart50, so it fit down the dry well shaft just fine. after the tank heated up to a working temperature, the gb142 sensor seems stuck in the drywell. is this just me being a little too cautious? or did the gb142 sensor expand more than the stock triangle tube one would have? in researching the buderus line of indirects, i notice the sensor is only partially inserted into the side of the tank, rather than through a long dry well on the triangle tube heaters. this also made me somewhat nervous for putting the buderus sensor down the triangle tube dry well...

also, i had to marrette the connection to extend the buderus sensor's length, to accommodate the distance between the boiler & the the dhw section of the boiler control is showing the same as before, with no indirect being detected. did i fry the sensor? or is the hot water in the tank just hotter than even the highest temp setting on the dhw section of the buderus?

(does all this make sense?) any help is appreciated!!!


  • IronmanIronman Member Posts: 5,817

    I'm not familiar with the term "marrette", so I'm not sure what you've done.

    All that is required to extend the wiring on the sensor is to splice it to 18ga. thermostat wire with wire nuts and then connect that back to the "FW" terminals on the low voltage board.

    You'll have to use a second circulator for the indirect loop and that should be connected to the "PS" terminals on the high voltage board.

    I've used the TT indirect with Buderus and never had any issues, but as you've discovered by trial and error, and as the applications manual makes clear, you've got to use the Buderus sensor.

    Your boiler requires a properly trained tech with a combustion analyzer to commission it and it also requires that it be piped, pumped and vented correctly. If your plumber was incapable of wiring it correctly, then I would doubt his ability to do the other things correctly. You have a sophisticated piece of equipment that requires more than hooking up a couple of pipes and wires, throwing on the switch and walking away. I would recommend that you call Buderus and see if thy can recommend a contractor in your area.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • jeffro83jeffro83 Member Posts: 10
    thanks for the reply

    sorry, by "marrette" i was just talking about wire nuts. so if the cable i've spliced to is a larger gauge, it might not work? i can just as easily go and buy 5-6ft of 18ga thermostat wire.

    as for another circ pump, yes there's a secondary dhw pump installed.

    yea, i agree; i was surprised that my plumber was so nervous about working on wiring...though he might just have been lazy (he spent a fair number of hours fixing what my last plumber screwed up). that said, i didn't know much about the buderus name when i had it installed 2yrs ago...and it seems, neither did the original installer. he assured me it was installed to spec, but i was working for most of the time he was in my basement. i've actually redone a few things he screwed up as well (condensate & venting issues).

    i've spoken to the folks at buders before, and from what i remember they said they still don't have any dealers anywhere near my city. the guy who originally installed the boiler had to "special order" it...probably from the internet. that said, of all the reputable plumbing and hvac shops in my city, NONE even recognized the buderus name.

    ...this is when i started studying the service/installation manual.

    as for the buderus dhw sensor, am i overreacting about the seemingly lodged sensor in the dry well of the smart50?
  • Mark EathertonMark Eatherton Member Posts: 5,843

    the tank down, and the sensor should come out.

    THe actual sensor that is embedded within the body of the sensor is about the size of a BB. You can grind a few thousandths off of the outside of the sensor without compromising anything major, and make it slide in a little easier.

    Using a larger wire is fine. 18 Ga I believe is the minimum recommended size.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • jeffro83jeffro83 Member Posts: 10

    sounds good, i can file down the sensor body.

    but if a larger gauge wire is fine...why did the boiler stop recognizing the dhw setup when i added the extension?
  • IronmanIronman Member Posts: 5,817
    edited August 2011

    That's a 10k ohm thermistor, which means it should read 10k @ 77*. Disconnect it from the boiler and check it with an ohm meter to see if it's good. It should read about 5k @ 105* and 2.2k @ 140*. Also check your wire and connections.

    Once you've established that the sensor is good, turn the power off to the boiler, then back on and set the left dial on the control to the temp you desire in the tank.

    Buderus now has a "Dealer Locator" on their web site. That may be helpful. Where are you located?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • jeffro83jeffro83 Member Posts: 10
    seems ok...

    didn't end up needing to check resistance...the tank had just gotten THAT hot, that it remained warmer than even the lowest setting for a day or 2. also checked with triangle tube about the stuck probe. they said if for whatever reason the sensor becomes toast, only then would i have to remove the dry well to remove the sensor. he didn't seem to think it was a problem that the sensor was stuck, as long as it was...sensing.

    thanks for your help, guys!
  • Mark EathertonMark Eatherton Member Posts: 5,843

    If you disconnected the sensor to add length, the controller dismissed the DHW function.

    When you reconnect it, I believe you MUST reboot the computer in order for it to recognize the DHW function again.

    As for sensor placement, if it is too shallow in relation to the tanks vertical profile, you will run out of hot water, because you are only using 1/2 of the tank. As long as you don't have any large dump loads (1 man 4 woman soaking tub) you should be fine.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • meplumbermeplumber Member Posts: 678
    Used this config many times.

    I have used this pairing many times.  It works.  The only advice that I have is to install an Anti-Scald Valve on the hot water.  These tanks seem to thermal stack more than others.  We have had several issues with the tank being at 120 at the sensor location, but closer to 140 and the top, where the hot water is drawn from.  Protect your family and install a mixing valve.
  • jeffro83jeffro83 Member Posts: 10
    thanks again

    yes, i did reboot the boiler when i did any wiring changes (i think it was just THAT hot in the tank that it didn't matter where i had the dhw thermostat set to). also, the stock TT sensor went right to the bottom of the dry well, roughly mid point of the heater. i've backed off the buderus sensor by about 1/2" so it's roughly the same spot, should be fairly accurate, i'd hope.

    also, thanks for the heads up, meplumber. i usually keep the thermostat set pretty low as it is, but i could see it being an issue if, for whatever reason, we decide to regularly set the water temp higher.
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