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Weil Mclain Steam boiler with 2 T-stat wires

Hi guys,

my current setup is a WM steam boiler with only two T-stat wires run from boiler to T-stat. I have read good things about the Ecobee 3 lite T-stat being used for steam as a smart T-stat and purchased one a year or so ago only to find out the age old dilemma about no common wire so I shelved the idea as I Was dealing with more pressing issues but it seems there is a relatively simple simple solution using the Fast Stat common wire maker.

I actually went ahead and ordered one so my question is two fold: What is the general consensus on using the fast stat gadget? Any down sides? I read it should not be utilized in walls with insulation as it gives off small amount of heat. My wall where T-Stat is located is an interior wall with no insulation so that should not be an issue I will just have to widen the hole a bit where the wires come out of the wall to fit the sender portion inside wall cavity

ok my 2nd question is a wiring question, my wiring on my boiler seems different then most but maybe this is because Wel Mclain does things different? From boiler I have the G terminal connecting to the R terminal on the T-stat side and the Y terminal connecting to the W terminal on my T-stat

Looking at the instructions for the Fast stat wiring I don't see this configuration. Any thoughts on how I should or could set this up?

still deciding if I Want to actually do this but it would really be nice to control the boiler remotely from the internet although it's not a must have.

From what I have read seems Ecobee handles steam pretty well. I have my current stat set to CPH= 1 so not sure how ecobee will handle this either..

AS always thanks in advance!!!

Chris

Comments

  • SteamBoiler
    SteamBoiler Member Posts: 90
    Look at my schematic on this recent thread for how I installed Nest on my Weil McLain with the thermostat supposed to connect between G and Y on the boiler board using an external transformer and isolation relay. I did have a common wire. I strongly recommend using the external transformer and isolation relay since the thermostat connections on the Weil McLain are downstream of the low water cut off unit and thermostat power is now dependent on LWCO solidly passing 24V. Additionally I had issues with my Nest trying to power steal for with spurious 3 minute heat calls even though I had the common and it was possible the WM wasn't just able to provide a robust 24V. Nest, Ecobee etc draw a good 200mA and not sure the boiler transformer can provide that reliably.


  • Chris_108
    Chris_108 Member Posts: 22
    edited December 2022
    Thank you Sir. That complicates things a bit for me (using an external transformer and isolation relay) as I am not well versed on this. Looking at my boiler inside panel I see there is a spot to pop in another relay/transformer right above where my existing relay/transformer is so I would put the new 24 volt transformer in there and the relay would go on there and only connection I would have to it would be the Common wire connection?

    Thanks again for your help/insight
  • SteamBoiler
    SteamBoiler Member Posts: 90
    edited December 2022
    Chris_108 said:

    Thank you Sir. That complicates things a bit for me (using an external transformer and isolation relay) as I am not well versed on this. Looking at my boiler inside panel I see there is a spot to pop in another relay/transformer right above where my existing relay/transformer is so I would put the new 24 volt transformer in there and the relay would go on there and only connection I would have to it would be the Common wire connection?

    Thanks again for your help/insight

    Chris, the diagram that I posted on the other thread is a wiring diagram, each hand drawn line is a wire. I got your message. I looked at the Fast Stat common maker install instructions and to be honest I don't see a way to have the Fast Stat, the 24V external transformer, and the isolation relay all work together. Check your RW wires at the thermostat and boiler ends to see if there is an unused wire that is cut short at both ends and just a stub. I was lucky to have a 3 wire cord from the boiler to the thermostat and 2 were used for R and W and one was unused and cut short at both ends so I could use it for C. If you don't have this 3rd wire, and can't run one, then the Fast Stat seems to be the best option and the instructions are quite clear. I would suggest doing the wiring with boiler power off so you don't short anything. It is possible that your Weil McLain boiler transformer is more robust than mine and will be able to power Ecobee reliably with the Fast Stat alone.
  • Chris_108
    Chris_108 Member Posts: 22
    Sorry don't know your name so I will just say Steamboiler, Yes unfortunately I only have two wires in total actually I have a third at either end but it doesn't seem to be the same wire - we tested and had an OL. So yes I bought the fast stat Common maker and plan to utilize it with my Ecobee 3 lite. My boiler is 10 years old is a Weil Mclain Peg - 55 200k BTU rated.

    Maybe I will try to wire it up as per Fast stat instructions and see if I have any issues with the ecobee cutting out on me. if it works I am done but if it cycles on and off I can explore the external transformer/relay option but did you say you don't see how this can be done while using the fast stat common maker?

    as always thank you,
    Chris
  • SteamBoiler
    SteamBoiler Member Posts: 90
    Additional note, yes, Weil McLain do want the thermostat wired between G and Y on their board. If you look at the ladder diagram section of the schematic you will see that R from the WM transformer goes to the Low Water Cut Off first, which if OK will pass 24V from boiler R to the thermostat R at the boiler G point. If thermostat calls for heat then the 24V (at thermostat, W) will be transferred to the boiler at the Y point. So the thermostat only gets power if the Low Water Cut Off is working properly and senses safe water level.
  • dabrakeman
    dabrakeman Member Posts: 552
    Yes but you can't let the thermostat lose power ever or it will reset and cause control problems.