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How to feed continuous power to Nest (Controller cuts power during DHW production and WWSD)

Swamp_Yankee
Swamp_Yankee Member Posts: 12
I have a Buderus boiler with the 2107 Logamatic controller. Way overkill for the application, a late 1800s farmhouse with baseboard heat, but I didn't put it in, the previous owner did. In any event, for those of you not familiar with the boiler and/or controller, when there is a call for DHW the controller cuts power to the zone valve controller entirely in order to devote all of the heat energy to making DHW. This plays havoc with the Nest thermostats controlling the zones in that when there is a call for DHW (bathing, clothes washing, dishes, etc...) the thermostats will shut down and I can't see what the temperature in that particular zone is or change it until the call for DHW is satisfied and power is restored to the zone valve controller/thermostat.

The even more annoying aspect of this is the 2107's warm weather shutdown function, which again, cuts all power to the zone valve controller. This drives me nuts during shoulder season because with the WWSD temperature set to say 60°F the 2107 cuts power during the day and then in the late afternoon early evening when the temperature dips below 60°F the 2107 restores power but the Nests have to charge up before they can operate, leaving the zone valves closed until they do. It's very frustrating. I should add that the Nests have the learning function turned off because it would interfere with the way the 2107 controller works. The Nests are essentially WiFi connected "dumb" programmable thermostats. I only installed them so that I can monitor and change the temperature from anywhere and/or with Alexa. I also just like the look better than the old LCD screen programmable thermostats they replaced.

The only wires I have to work with are R and W1 which are connected to the Nests. If there were other wires in the bundle they were clipped back too far in the wall to see. As I mentioned earlier its a very old house so fishing a new wire for the downstairs zone would be a ****, fishing a new wire for the upstairs zone would basically be impossible. The Nests do have a micro USB charge port in the rear but it can only be accessed when the unit is off of the wall. At this point I would be willing to connect some kind of auxiliary battery pack that I had to periodically change (just like an old programmable thermostat) because I'm so sick of dealing with dead Nests. Any ideas?

Comments

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,188
    There is probably no easy fix from Nest or from your controller manufacturer. The only thing I can think of is Isolation relays where a transformer dedicated to the Nest and the relays is always on and the relay contacts do the actual switching. It's a hassle but I did it for a customer in Cape May NJ a few years back. I needed a Heat Relay, A Fan Relay, and a Cool relay for two thermostats on the same controller. (6 relays total) The other 4 Nest thermostats in the house were not on that controller and were compatible with Nest.

    For more info. message me.
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • Ironman
    Ironman Member Posts: 6,400
    Wire the ZVC so that the transformer is hot all the time and let the 2107 break power to the circulator after it goes through the end switch (X X) contacts of the ZVC.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    STEVEusaPA
  • STEVEusaPA
    STEVEusaPA Member Posts: 5,115
    edited October 2020
    Nest just doesn’t belong on a Buderus with a Logomatic. You have 2 brains banging into each other. The high functioning Logomatic vs. th POS-KnowsNothingAboutHvac-Nest.
    Properly designed and commissioned your boiler only needs a thermostat as a high limit if you dialed in your outdoor reset.
    Run the Buderus as designed-no setbacks, no fancy thermostat, get a plug in transformer and use the Nest to monitor room temperature, disconnected from the boiler.
    steve
    IronmanHVACNUTGordoSuperTech
  • Swamp_Yankee
    Swamp_Yankee Member Posts: 12
    Ironman said:

    Wire the ZVC so that the transformer is hot all the time and let the 2107 break power to the circulator after it goes through the end switch (X X) contacts of the ZVC.

    This sounds like the easier solution since all of the wiring would be done in the basement, but I wouldn't feel comfortable attempting it myself. I may contact a local pro to see if he could do it.

    Properly designed and commissioned your boiler only needs a thermostat as a high limit if you dialed in your outdoor reset. Run the Buderus as designed-no setbacks, no fancy thermostat, get a plug in transformer and use the Nest to monitor room temperature, disconnected from the boiler.

    That's pretty much how I have it set up-the Nests have the learning and energy saving modes turned off, so again they are basically WiFi connected "dumb" thermostats. We pretty much use them to dial back the temperature during the day at times because we have a lot of glass on the south side of the house on both floors. On a clear sunny winter day it can get too warm in the house we will back off the thermostats. However, on a cloudy winter day we'll leave them alone and let the 2107 do its thing.


  • Ironman
    Ironman Member Posts: 6,400
    Here’s the diagram. You’ll need one additional wire between the 2107 and the ZVC.


    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    HVACNUTSwamp_Yankee
  • Swamp_Yankee
    Swamp_Yankee Member Posts: 12
    edited October 2020
    This is the inside of my ZVC-anyone want to try to walk me through it?

  • Ironman
    Ironman Member Posts: 6,400
    Remove the black wire from the "COM" terminal on the terminal block next to the "End Switch" and get rid of it or cap it off with a wire nut.
    Then run a wire from terminal "63" on the 2107 to the "Com" terminal where you removed the black wire.

    It's that simple.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    STEVEusaPASwamp_Yankee
  • Ironman
    Ironman Member Posts: 6,400
    Edit:
    I missed one step:
    The black wire on the "Com" terminal goes into a wire nut with a group of black wires. One of those is presently connected to "63" on the 2107. Move it from "63" to "L1" on the 2107.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Swamp_Yankee
  • Swamp_Yankee
    Swamp_Yankee Member Posts: 12
    edited October 2020
    Ironman said:

    Edit:
    I missed one step:
    The black wire on the "Com" terminal goes into a wire nut with a group of black wires. One of those is presently connected to "63" on the 2107. Move it from "63" to "L1" on the 2107.

    So just to confirm, I can disregard your first post-the black wire on the COM terminal stays where it is, I just need to open up the back of the 2107, find terminal 63 remove the wire, and move it to terminal L1? Just trying to be doubly sure before I do this-don't feel like buying another 2107 :#
  • Ironman
    Ironman Member Posts: 6,400
    No, use the info in both posts.

    The problem is that the "63" pump terminal is now feeding the transformers and the pump in the zone panel. We only want it to feed the pump through the "Com" and "No" terminals of the zone panel.

    The transformers need to be fed from "L1".
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Swamp_Yankee
  • Jamie Hall
    Jamie Hall Member Posts: 16,326
    Um... the easiest fix is to sell the Nests on Craigslist and put in a good thermostat or two...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    GordoSuperTech
  • Swamp_Yankee
    Swamp_Yankee Member Posts: 12
    Ironman said:

    No, use the info in both posts. The problem is that the "63" pump terminal is now feeding the transformers and the pump in the zone panel. We only want it to feed the pump through the "Com" and "No" terminals of the zone panel. The transformers need to be fed from "L1".

    I think I get it now-the diagram you posted is as the wiring should be in order to eliminate the DHW priority mode, not as it is now.

    Um... the easiest fix is to sell the Nests on Craigslist and put in a good thermostat or two...

    Truth be told I will probably be swapping out the Nests for Ecobees eventually because they will allow me to control my mini split AC units as well (the Nests will not), but the Ecobees (or any similar thermostat) would be plagued by the same power loss issue unless I rewire it as Ironman stated.
  • Ironman
    Ironman Member Posts: 6,400
    The diagram is how it SHOULD be wired.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
    Swamp_Yankee
  • Swamp_Yankee
    Swamp_Yankee Member Posts: 12
    Finally got around to opening up the 2107 and changing the wiring around. The only snag was that on the L1 terminal I had to use a female spade connector because it didn't have a screw terminal lug like all the rest. Now my Nests are fully charged all of the time and working perfectly. Thanks again all for the assistance-now I'm just waiting patiently for Dan's next installment of Dead Men Tales!
    Erin Holohan Haskell