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Help with wiring ECOBEE thermostat with 18/3

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TheClevelandSteamer
TheClevelandSteamer Member Posts: 26
edited 2:49AM in Strictly Steam

We have a gas-fired Weil-McLain EG55PIDN series 4, 2001 model in good working order, and serviced annually. Two pipe system with 19 radiators, all in good working order with fresh traps and valves.

We would like to upgrade our thermostat to an Ecobee Smart Enhanced model with Wi-Fi capability, so that we can monitor temperatures and turn the boiler on/off remotely.

The existing thermostat is connected via 18/2, using a red and white ran a new 18/3 wire.

There's a 24 V transformer as shown in the photo below below, with the following terminals:

IMG_9212.jpeg


Y - connected to the white thermostat wire

G - connected to the red thermostat wire

C

W

Trans Sec

There's also a Honeywell SB8610U ICM continuous retrywith several of terminals. There's also water feeder and an LWCO, which I certainly don't want to bypass.

IMG_9211.jpeg


The new Ecobee thermostat won't turn on without the green wire connected, and I'm having difficulty figuring out which wire terminal to connect it to.

I haven't powered it up yet I don't want to damage it by connecting it under the wrong terminal.

Can someone kindly advise me as to which terminal to connect the green wire to get power to the thermostat? Or do I need an isolation relay to get power to it?


Thank you.

Comments

  • pecmsg
    pecmsg Member Posts: 7,537

    you ran a New 18/3wire?

  • 109A_5
    109A_5 Member Posts: 4,454
    edited September 26

    This is hopefully a similar wiring diagram to your boiler, although you probably don't have a standing pilot.

    Is your LWCO a probe type ? If so the first thing connected to the Transformer's R terminal is the LWCO and not the thermostat.

    You will probably need to add relay. Since the LWCO and the Ecobee thermostat both want constant 24 VAC power.

    The Ecobee thermostat's R and C would connect to the transformer's R and C. This provides constant power to the Ecobee. The coil of the added relay would go to the Ecobee's W terminal and the transformer's C terminal. The contacts of the added relay would connect to where the original 2 wire thermostat was connected. I bet @EdTheHeaterMan has a wonderful wiring diagram all ready prepared as to how to add the relay.

    image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • TheClevelandSteamer
    TheClevelandSteamer Member Posts: 26

    Yes, original Thermostat was in a less than ideal location. We relocated it to a different room, and while we were at it, we ran a new 18/3 wire.

  • Steamhead
    Steamhead Member Posts: 18,878

    @109A_5 is correct, you'll need a relay. Any good relay with a 24-volt coil should be fine. I like these:

    https://www.supplyhouse.com/Resideo-R8222B1067-24V-General-Purpose-Relay-with-SPDT-Switching?utm_adgroupid=177827080713&utm_targetid=pla-304229468133&utm_product_id=R8222B1067&utm_matchtype=&utm_adtype=pla&utm_category=Heating&gad_source=1&gad_campaignid=22340288845

    https://www.supplyhouse.com/Resideo-R8222D1014-24V-General-Purpose-Relay-with-DPDT-Switching?srsltid=AU7gw4Xku8dWswZL5xNkHq3e2GQSV7JbShnKdCk8hv8mOG6FFDIpxr-E

    Co-Founder, All Steamed Up, Inc.

    Semi-retired

    Baltimore, MD, USA

  • 109A_5
    109A_5 Member Posts: 4,454

    Another method illustrated here is to use a second transformer to power the Ecobee.

    image.png
    National - U.S. Gas Boiler 45+ Years Old
    Steam 300 SQ. FT. - EDR 347
    One Pipe System
  • Steamhead
    Steamhead Member Posts: 18,878

    That method works well on hot-water systems with zone valves, because of the extra transformer capacity. The relay isolates the ZVs from the boiler, eliminating the chance of getting wires crossed and frying the transformers.

    Co-Founder, All Steamed Up, Inc.

    Semi-retired

    Baltimore, MD, USA

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 12,734

    That is why I posted that diagtam where it is easy to find. Thanks @109A_5 for sharing it. But somehow there is a black line where some wires should be. Here is the corrected version.

    image.png

    I also went back to the original post and corrected it too. Thanks Again @109A_5

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

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