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3-wire Nest to WM EG boiler?

JohnNYJohnNY Member Posts: 1,822
I tried posting in Controls but got crickets.

Can anyone help me out with a wiring diagram or written description for 3-wire thermostat to an EG boiler?

Many thanks,

For private consulting services, find John "JohnNY" Cataneo here at :
"72°F, LLC"
Or email John at [email protected]
Or at Gateway Plumbing & Heating
John travels regularly to out-of-state clients for consulting work.


  • heatpro02920heatpro02920 Member Posts: 991
    edited May 2014

    I seen this in controls, but wasnt sure what you were asking, I am guessing you want to power the nest so it will charge itself?

    If so wire rw as you would normally and wire c to the other side of the transformer...

    On the nest I believe it is the top W, then c is in the middle, and then RH is at the bottom all on the right side... All you are doing is giving the t stat both legs of your 24v instead of just one leg, in other words normally a 2 wire tstat just has say the negative leg and it breaks it or makes it, it acts like a switch...

    Now you want to power the tstat with it so you need both legs pos and neg, so you need to bring that up from the source of the 24vac, so wire it to the other leg... Find the transformer, and hook C up to the missing leg...
  • Paul SPaul S Member Posts: 1,228

    Are you sure what turns the boiler "on" is a basic 24v  "T&T"......JUST the other day a knucklehead sold a "NEST" thermostat, boiler was one of those LAARS ENDURANCE EBP HOT WATER BOILERS THAT SIT IN A CLOSET...basically its a TOUGH spot to work......3hrs to change relief valve and extrol#15.....BUT on on one occassion i used a simple DPDT OR SPDT general purpose relay (r8222d)??? I think i used a SPST GPRELAY i used one of the normally open contatcs to turn boiler on (T&T).....I WIRED IN A NEW 40VA TRANSFORMER , the TRANSFORMER JUST POWERS THE TSTAT CIRCUIT and the GPR coil ......R from TRANSFORMER goes through R on tstat then when theres a call for heat 24v will go through W to 1 side of gpr relay coil other side to common.....then N/O contacts on relay to T & T.......paul s
    ASM Mechanical Company
    Located in Staten Island NY
    Servicing all 5 boroughs of NYC.
    [email protected]
  • heatpro02920heatpro02920 Member Posts: 991
    edited May 2014
    That eg should be 24v

    I believe. if not paul is correct you can use a sr {the tacos have 24v aux} or depending on the setup the nest can be configured to just be powered during a call for heat {I dont know how well this works}, but if you have a milli system or something that you can not grab 24v from {or your manufacturer doesn't allow it, I think Buderus states it will void warranty to use power consuming controls off of their systems} you can use a RIB...

    heres a quick drawing, you will of course need a 24v trans and a rib spst... BUT the EG should be 24v, now if wm voids warranty for using a tstat with a load I don't know...

    RIB u1c is the rib number I believe and any 24vac sec 120v pri transformer will do the trick, I have used the off the shelf 40va's a bunch of times to power t-stats... My coal furnaces entire control system is ran off a 40va with rib's, controls all the tstats, feeder motors, zone damps, ect...
  • JohnNYJohnNY Member Posts: 1,822
    Thanks, guys

    This is one of those things I just haven't dealt with much.
    For private consulting services, find John "JohnNY" Cataneo here at :
    "72°F, LLC"
    Or email John at [email protected]
    Or at Gateway Plumbing & Heating
    John travels regularly to out-of-state clients for consulting work.
  • heatpro02920heatpro02920 Member Posts: 991
    I do the same thing, when I haven't seen something in a while

    yesterday I had to wire a 6006 into a 8148j so they had a low limit, I could not for the life of me remember exactly how to do it, I had to look it up but couldn't find the info anywhere, so I had to trial and error it until I got it rite, 3 trys was the magic number, I know with the 8148a its simple just wire R to r1 take out the jumper to 3 and wire 3 to the center wire of the 6006 then the bottom wire to the top of the 8148a's limit dials terminals, with a j its almost the same except, remove the jumper from w to z and jump z to tp hooking them to the center of the 6006, confusing to say the least, now I wont do it again for 8 years and I will have to figure it out all over again... Ill have to look up this post to remember...
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