How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Phil Your Own Question
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
Type Your HVAC Question Here...
Phil is online now
A new question is answered every 9 seconds

I have a nest thermostat I'm trying to install. I replaced

Customer Question

I have a nest thermostat I'm trying to install. I replaced the wiring because my old thermostat had 3 wires and it looked like i need a common wire. I need help connecting the wires to the boiler controller in the basement but I don't know where to connect the common wire.
Submitted: 9 months ago.
Category: HVAC
Expert:  airheatman replied 9 months ago.

Cam you give me a bit more information.

1/Tell me what model as on old tstat

2.Tell me what wires went to what terminals

3.Give me model on boiler/controller

4.Tell me where wires attached at controller.

Any pictures would be helpful.

If you have a paper clip icon on your page you can attach using that link.Or

You can upload the pictures using the tiny pic site .

Here is a link to the site.

Click on Browse , select the file from your folder.then click UPLOAD NOW.

They will give you a quote to enter in the box to verify you are a human.Enter the quote and click UPLOAD NOW

You will see your picture on right side of screen.

Then copy the link URL for email & IM

Paste that link here on the site.

Customer: replied 9 months ago.
thank you for helping me out. Ok. the old thermostat model is a Robertshaw CM250. There were 3 wires going to that thermostat a white wire going to the W terminal, a red wire to the R terminal and a green wire to the B terminal. I'll add a photo of it to the url. The boiler is a Enerjet model number BG-4 and the controller is a honeywell Aquastat model L8148J. The wires are green to TV terminal, White to W and Red to the T terminal. I had a blue wire I want to use as my common on the Z terminal because I was told I could use it as a common but it didn't work so it disconnected it. Sorry for the late replay. thank you again
Customer: replied 9 months ago.
Customer: replied 9 months ago.
Customer: replied 9 months ago.
Customer: replied 9 months ago.
Expert:  airheatman replied 9 months ago.

Give me a few minutes to look this over.

Expert:  airheatman replied 9 months ago.

OK I could probably help you figure this out, but not really familiar with the boiler.I am going to open this to other experts who may have answer readily available.If not I will come back and help you with it.

Customer: replied 9 months ago.
ok thank you

Related HVAC Questions