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CU3A questions

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GW
GW Member Posts: 4,701
Anyone having any issues with the Viessmann CU3A holding its schedule on the A circuit? The boiler simply isn't moving heat when the program is clearly looking for warmer temps. The local rep says there will be a swing (it won't follow the schedule exactly due to its inherent swing I guess). We have a Vitotrol 200A set up for constant circ. I did many WB2Bs like this and never got a call. Thanks for any comments.
Gary Wilson
Wilson Services, Inc
Northampton, MA
gary@wilsonph.com

Comments

  • Paul Pollets
    Paul Pollets Member Posts: 3,656
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    Is the heating curve high enough? If the timer function isn't bringing the system temps to required setpoint, the computer may have a glitch.
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,050
    edited April 2018
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    We have an on-going problem with a Vitodens B2HB set up for constant circulation and Vitotrol 200A. In the middle of the night, the boiler turns off the secondary pump.

    We've checked the schedule and all of the coding; replaced the coding plug, did a hard re-boot......... nothing works. We even disconnected the 200A and reset the coding; same thing.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
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    That has to do with Coding at B5. There may be a software glitch that requires a new control. You may want to get the local rep involved.
  • gennady
    gennady Member Posts: 839
    edited April 2018
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    Does boiler piped p/s?
    Are there other system loops ?
    I never had this problem with these.
  • GW
    GW Member Posts: 4,701
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    It’s not piped PS. This is a big boiler. I have a constant circ and a zoned circ with zone valves.

    We added a LLH sensor (there is no LLH so I use that term lightly) and the boiler tracked the schedule like an arrow for 3 or 4 days, then the temps drifted again.

    I’ll look at the B2 and the B5 again. I didn’t ask my tech to check these when he installed the pipe sensor

    Alan are you running a LLH sensor?
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Tinman
    Tinman Member Posts: 2,808
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    I agree with Gary. The CU3A holds a lot of water. I'd be hard pressed to see why a boiler pump would be necessary.
    Steve Minnich
  • Alan (California Radiant) Forbes
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    Alan are you running a LLH sensor?

    Yes.

    I've been over the problem with technical support, a few times. I also talked to the trainers while I was in Warwick. Nada.

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Tinman
    Tinman Member Posts: 2,808
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    That's discouraging!
    Steve Minnich
  • Alan (California Radiant) Forbes
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    I normally power the system pump from the zone valve controller, but this time (for various reasons), I connected it to the 28/20 plug in the boiler and changed coding address 53 to a value of "2".
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • GW
    GW Member Posts: 4,701
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    Paul if the outdoor temp is below the setpoint the pump should be running, at least that’s my understanding. I’ll look at the settings again
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
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    There's no need for a primary pump on this boiler. Nor is the LLH needed which is one of the big selling points...no hydraulic separation needed. The B5 code controls the setpoints and it may be just a matter of getting the right code programmed. If the device won't follow the B5 setting, the control should be replaced. This is presuming the boiler was piped to manufacturer's instructions.
  • gennady
    gennady Member Posts: 839
    edited April 2018
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    what is the setting at address 51? 52? 53?
    A5? What plug pump connected to, 28/20 or 20?
  • GW
    GW Member Posts: 4,701
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    Gennady If you have some general opinion what the settings should be can you please share them, I’ve been back on this several times and I’m desperately trying to keep my trips to a minimum, for a couple reasons.

    Thanks, Gary
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Simply Rad
    Simply Rad Member Posts: 184
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    Gary, have you checked coding 2 address 90? Time interval for taking outdoor temperature into consideration?
    Jeffrey Campbell
  • GW
    GW Member Posts: 4,701
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    No i haven't looked at 90.

    I did get a hold of Canada and went make to make another round of tweaks. I will look at the manual and see what 90 is all about.

    Thanks for the help.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • RGB
    RGB Member Posts: 1
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    I had a similar problem turned out taco 007e pump shut down after 12 hours . No mention of it in the instructions , taco factory rep told me to switch the pump out with a different model.
  • GW
    GW Member Posts: 4,701
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    wow that will do it too :)
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com