converting 2 wire T-Stat to Wi-Fi Tstat ( have spare wires)

[Mikepier]

Hello. I currently have a Honeywell standard display T-stat. It has only

2 wires connected to the R & W terminals to control my Weil-Mclain steam bo iler. The T-stat is battery operated.

I have spare wires in my current T-Stat wiring which I would like to utiliz e to hook up a Wi-Fi T-stat. The Honeywell rep I spoke to in tech support s aid to put the 2 existing wires to the R & W terminals, and to connect a se parate 24VAC Power source ( which I have in my basement) to the C & RH term inals, with all jumpers removed.

Just wondering does this sound correct?

[Tony Hwang]

Hi, When you get the new 'stat, the installation manual will clearly show how to hook up that wire. It'll have diagram. I did same with Eco Bee 'stat for my daughter's cabin in the mountain. You don't believe Honeywell tech support guys?, LOL! I retired from that company after ~40 years. If you ask same question with email they may attach diagram in reply. Or you can download manual in advance to double check it.

[gfretwell]

Your stat is operating as a simple 2 pole switch. The Red is 24v in and the white is "heat call" out. The common is in the boiler.

You could use an unused wire to bring the common to the WiFi thermostat from the transformer, hook it to C and you are done.

[trader_4]

y 2 wires connected to the R & W terminals to control my Weil-Mclain steam boiler. The T-stat is battery operated.

lize to hook up a Wi-Fi T-stat. The Honeywell rep I spoke to in tech suppor t said to put the 2 existing wires to the R & W terminals, and to connect a separate 24VAC Power source ( which I have in my basement) to the C & RH t erminals, with all jumpers removed.

+1

As you say, the only thing it needs to power a smart thermostat is one additional wire to the common. And as Tony said, the instructions, which should be available online should confirm that.

[N8N]

y 2 wires connected to the R & W terminals to control my Weil-Mclain steam boiler. The T-stat is battery operated.

lize to hook up a Wi-Fi T-stat. The Honeywell rep I spoke to in tech suppor t said to put the 2 existing wires to the R & W terminals, and to connect a separate 24VAC Power source ( which I have in my basement) to the C & RH t erminals, with all jumpers removed.

What he said.

Use a black wire if you have it for the common.

nate

[Mikepier]

OK, I got it hooked up ,and its working great. But I have a question concer ning the wiring from my steam boiler. Attached is the wiring diagram. My bo iler is on page 8.

As you can see on the ladder diagram, The T-stat R wire ( which in this cas e is terminal G on boiler terminal block) is going through the low water cu t-off feed.

So this means that everytime the LWCO calls for water, which is not often, the power to the t-stat gets killed because the relay opens up, which I und erstand this is the way its suppose to work for safety. I confirmed this by testing yesterday, I drained boiler until light on LWCO kicked on. Is there any way around this? Not a big deal, but just curious.

[trader_4]

erning the wiring from my steam boiler. Attached is the wiring diagram. My boiler is on page 8.

ase is terminal G on boiler terminal block) is going through the low water cut-off feed.

, the power to the t-stat gets killed because the relay opens up, which I u nderstand this is the way its suppose to work for safety. I confirmed this by testing yesterday, I drained boiler until light on LWCO kicked on.

The obvious way around it would seem to be to not wire it in series with th e low water cut-off switch. But I don't understand what the issue is. If th e boiler is working properly, the boiler should maintain the proper water level. If it's not, then you want the boiler shut off because it's a hazard, which is what the install intruction wiring would seem to be doing .

[Mikepier]

Well, a steam boiler will always lose some water normally, so it's always going to need to be refilled. Not often, but it is normal.

[trader_4]

Doesn't it have an automatic fill? And regardless, if the water gets so low that it triggers the low water cut-off, why would you have an issue with the thermostat being wired in series with it? It sounds like they open the thermostat circuit to keep the boiler from firing when the water is too low.