Nest with a 2-wire 24V boiler

[dane64]

I have an old mercury thermostat that I'd like to replace. There are two grey wires that are unlabeled. I've measured 24V between the two wires.

Will a nest work without the separate 24V adapter?

If it will work without the adapter, which terminals should I connect the (+) and (-) wires to on the Nest?

Thank you!

[Markjosephp]

Hi dane64,

I'm sorry for the delayed response, and thanks for reaching out. I'd like to take a look into this for you.

Could you please share a picture of the wiring configuration in the unit's control panel so that we can determine compatibility? Also, please check the make and model of your boiler.

I'll look forward to your response.

Best regards,

mark

[dane64]

Hi Mark -

Many thanks for getting back to me. Unfortunately when I try to upload images I'm getting a message saying "you do not have permission to upload images" so I'm unable to do so.

However, I can say the following...

• The existing thermostat is a homemade project... it's not something you can buy in a store. It mostly works, except when it doesn't. The terminals are unlabeled. The two wires are both grey color, so no hints there. There's a relay that makes a connection between the two wires when the thermostat calls for heat. It's 24v across the terminals. The thermostat electronics are powered by USB.
• The boiler is a Burnham "independence boiler". It's steam heat.

Hope that offers a couple of hints!

best,

dan

[Markjosephp]

Hey there,

I appreciate your efforts, Dan. I can tell that two wires are for the power and heat, but we can't determine which of these two are for the heating and power terminals for the Nest Thermostats. Also, a C wire or a Nest Power Connector might be needed for additional power.

To be sure, I'd suggest contacting our installation partner, OnTech, to help you check your system’s compatibility, install, and set up your Nest Thermostat. After they’ve installed your thermostat, they can give you a demo and answer any questions you have.

Please let us know if you have more questions.

Best,

Mark

[dane64]

Thanks, Mark. I very much appreciate the effort.

best,

dan

[Markjosephp]

Hello dane64,

You're most welcome; I'm glad to help!

It looks like we have come to a solution, so I'm going to lock this thread in 24 hours. If you have any other concerns or questions, please feel free to create a new post.

Thanks,

Mark