Wiring Help: Honeywell Wifi Thermostat

Old 09-07-14, 11:14 AM
Thread Starter
Join Date: Sep 2014
Location: United States
Posts: 1
Received 0 Votes on 0 Posts
Wiring Help: Honeywell Wifi Thermostat

So I just picked up a Honeywell Wifi RTH9590 and tried to install it but I am completly stuck and thinking I might have to return it.

So my current setup is just heating. I have oil / baseboard. The wires coming up from the boiler is just 2 wires, RH and W.

Here is a pic from the heaters control panel

Name:  thermo.jpg
Views: 864
Size:  37.4 KB

The instructions for this unit clearly state I need a C wire. Well I am only trying to use this for heat, as I have a in wall AC unit.

Anyway to make this work? Please help
Old 09-07-14, 01:25 PM
firedawgsatx's Avatar
Join Date: Jul 2013
Location: USA
Posts: 1,726
Received 2 Votes on 2 Posts
Here is a link to a recent thread that discusses how you may be able to install an external 24V transformer to supply power for the C terminal on your new thermostat:


Here is a link to a manual: http://pdf.lowes.com/useandcareguide...890762_use.pdf

Looking at the instructions for alternate wiring on pages 16-17 it seems like it should be relatively easy to do with an external transformer.

What type of thermostat are you using currently?

Last edited by firedawgsatx; 09-07-14 at 01:48 PM.
Old 09-07-14, 01:46 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 70,075
Received 2,955 Votes on 2,666 Posts
Welcome to the forums.

There may be a C connection at that Honeywell control but we'd need a larger pic of the whole thing and the part number. It would be LA-XXXX

You would still need a third wire to the thermostat from that area.

If you choose to use a separate power supply to run the thermostat - you could use any 24vac 20watt unit.

24vac transformer power supply | eBay
Old 09-08-14, 05:19 PM
Geochurchi's Avatar
Join Date: Nov 2012
Posts: 5,583
Received 154 Votes on 140 Posts
Can you fish a wire from the boiler to the Tstat location ,maybe using the existing cable as a pull string,if so post a pic of your boiler controls,the best way is to use the existing transformer on the boiler.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: