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I am trying to connect a Honeywell T5 wifi thermostat to a…

I am trying to...

I am trying to connect a Honeywell T5 wifi thermostat to a system that doesn't have an existing "c" wire.

Contractor's Assistant: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?

Thermostat

Contractor's Assistant: Do you plan on doing the work yourself?

Yes

Contractor's Assistant: Anything else we should know to help you best?

I have a S8610U control unit.

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Answered in 2 minutes by:
9/10/2017
Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 24,391
Experience: 40+ yrs. experience as a licensed oil & gas technician.
Verified

Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your

issue. First I’ll need some more info so I have a more complete picture of your situation.

What is the brand and model of the furnace/boiler?

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Customer reply replied 10 months ago
It's a Peerless Series 61
Customer reply replied 10 months ago
The wire package running to the thermostat is only two wires.

Ok, you have to pick up the 24 volt comm (C wire) at the boiler transformer. You have to identify which of the 2 transformer lines goes to the R terminal on the thermostat. The other terminal is the common. You connect your C wire there. The wiring diagram shows the R lead as blue and the common as yellow. I wouldn't relay on this but it's a good place to start.

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Refer to my previous answer

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Customer reply replied 10 months ago
Do I have to run a third wire or can I accomplish what you suggested with the two conductor wire that is in place now?

You need a 3rd wire

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Customer reply replied 10 months ago
On the old thermostat, the two wires were connected to the "w" terminal and the "rh" terminal. I am guessing that I should just leave those going to those same terminals on the new thermostat. Is that correct?

Yes, but you need to be sure the one on R (=Rh) is the one from the transformer or the thermostat won't power up.

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Customer reply replied 10 months ago
Sounds good. Thanks Rick!!! Have a great night!

You're welcome

Rick
Rick, HVAC Supervisor
Category: HVAC
Satisfied Customers: 24,391
Experience: 40+ yrs. experience as a licensed oil & gas technician.
Verified
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