Common (C) Wire 24VAC for VisionPRO TH8110 with RedLINK

ktccapo

I'm currently running a Honeywell VisionPro TH8110U on a single-stage, oil-fired steam system. I've attached photo of the two wires coming off of the transformer (red and blue), and a photo of where they're connected to the TH8110U (red wire terminal R, blue wire terminal W).

I'd like to connect a new VisionPro TH8110 directly to the boiler, and still be able to utilize the REDLINK Internet Gateway. The manual calls for a Common, or C wire connection in such case.

As I currently only have to two wires to work with, can I simply use the red wire for the Common/C wire connection (attach it to the C terminal as opposed to the R terminal on the new TH8110)?

Any advice is much appreciated. Thanks and best,

KTC

ratio

You need a third wire for the C. It's the return for the 24 volts, to give the stat continues power. I suspect it's necessary because the RedLINK radio would go through batteries too fast.

A solution might be to install an EIM on the boiler & repurpose the two wires to power for the 8110.

ktccapo

Morning, thanks for the reply. As per your suggestion on the EIM, the model you pointed out only works with the FocusPro line...could I accomplish the same thing with this model ?

Also, in terms of a repurposing the two current wire to power the 8110, how exactly would that look? I'm assuming the the current Red and Blue off of the transformer (as per photos) would go to power the R and W terminals on the EIM, respectively?

Many thanks again and best,

KTC

Jamie Hall

If your thermostat needs a common -- C -- wire, you must have three wires, one way or another. Two of them -- from the transformer -- are 24 volt AC power to the thermostat. The third is switched by the thermostat to send a 24 volt signal to the boiler to operate. There is simply no way to do it without three wires.

ratio

Huh. I never noticed that the THM5320 was FocusPRO only. I sure thought I'd used it on 8000s before, but now I'm not sure. In any case, the THM5421 should work, although it's enough overkill that I'd call Honeywell to double check that the THM5320 won't work.

It doesn't look like the burner control exposes a C terminal, so you might have to add a transformer to power the EIM & stat if you can't figure a way of making one. After that, the T1 & T2 terminals would go to the rh & w terminals on the EIM (remove the jumper on rh first), then apply 24 volts to the EIM, use the old red & blue wires to feed the r & c terminals on the stat from the r & c terminals on the EIM marked "to thermostat". It looks like you have a remote sensor attached to your stat, you should be able to move that over to the new stat, make sure you program it in to the new stat.

ktccapo

Good morning,

Many thanks again for your assistance in helping me to troubleshoot this issue.

Given your details above, combined with what I've gleaned from the installation manual from the THM5421, which you can find here, I'm under the impression that I can solve my problem by just installing an EIM, as you described.

In so doing, I would not need to use another 24 V transformer, like this one, correct?

If I DID have to use another transformer, where would it fit into the wiring you already described?

Thanks again and best,

KTC

ratio

The EIM, as well as the stat, will require a C (common) and R (24 volt hot) conductor. I looked up the burner control from the pic you posted, and it doesn't seem to have a C terminal that is available externally. It's most likely that you'll have to install a transformer to make this all work. It isn't hard, but if you're uncomfortable with the thought, get help from someone.

If you do want to try to add the transformer yourself, it may have four wires, or perhaps two wires & two terminals, depending on the style. Using the first as an example, after switching the burner control OFF at the circuit breaker, the white from the xfrmr will connect to the white incoming to the burner control from the panel, & the black to the black incoming. At this point, the yaller will be the C (common), and the yaller with the white stripe will be the R (24 volts). Use these to power the EIM and the stat. You will then need to remove the jumper connecting RH to RC & discard it, then take T1 from the burner control to the RH terminal & T2 to the W terminal.

Do you have air conditioning, perhaps running from a different stat? It might be possible to integrate that operation as well.

Also, there are a number of settings in the stat that should be configured for best performance. In particular, don't forget about the remote sensor.

ktccapo

Hi Ratio,

Just wanted to reach back out to you to let you know that I did tackle the install of the transformer, EIM, and VisionPro 8000 with Redlink on my own...and with your advice, all seems to be working well. MANY THANKS!

I did nonetheless want to ask one follow up question. In connecting the T1 and T2 terminals to the RH and W terminals on the EIM, respectively, I included the two wires coming from the stand-alone Aquastat (photo attached).

In the original installation, the T1 (red) and T2 (blue) went directly from the Burner Control to the Tsat; the T1 (red) and T2 (blue) from the Aquastat were bundled and wire-nutted in, six wires in total (three red, three blue).

In my installation, I separated out the red and blue going to the Tstat, and repurposed it to power the new VisionPro from the R and C terminals of the EIM, as you advised.

Then, I recombined both T1 reds (Burner/Aquastat), both T2 blues (Burner/Aquastat), and attached them to the RH and W terminals on the EIM, as you advised.

So I guess the point of my question is as follows: should the T1 (red) and T2 (blue) from the Aquastat have instead been combined with the R and C from the EIM powering the VisionPro?

Everything seems to be working as it should, with the boiler calling for hot water when necessary, etc, so I'm assuming my connections are (somewhat) correct. Just don't want to risk a fire if I've got the wires mixed up.

I've attached a few photos, please let me know, and thanks again. Best,

KTC

ratio

Hmm. I'm not quite sure what the purpose of the aquastat is. What temperature is it set at?

ktccapo

It's set at 130 degrees...can be set either higher or lower, adjusted with dial.

Just to clarify, this is an oil-fired steam system where the boiler also provides hot water (there is a holding tank with circulator, photo attached).

Within 3-5 minutes of someone taking a hot shower in summer/fall, the boiler kicks on...less often in winter when system has been calling for heat all day...seems to still be working as such with new set up...

ratio

Ah, that makes sense now. It sounds like everything is the way it's supposed to be. I was wondering about the aquastat because what you described above meant that it could turn the boiler on as well as the thermostat, but as it turns out that's what is needed.