I've recently purchased 2 Nest Thermostat for my new place which has a thermostat downstairs and one upstairs. Doing my research it seems I'm going to need a C wire for them to function correctly the current thermostats are only 2 wire.
Looking at my setup I have a transformer, Honeywell relay, 2 Honeywell zone valves and a Navien NCB-240E combo-boiler as seen below.
I managed to review the wiring and excuse my diagram below but it was my best effort with microsoft paint.
Note: On thermostat #2 the black and white wire are twisted onto each other as one.
WC = Wire Cap (just the wires twisted onto each other with a orange wire cap on as seen in the photo)
After the couple of days of research online I believe in order to add a C wire for the nest thermostat i would just need to run the unused green wire on thermostat #1 and thermostat #2 to the W cable off the transformer which goes to WC5. Is this correct or am I far off?
If i was unclear i apologize in advance and will do my best to further explain if needed.
Nice diagram. I snagged it and added to it. I removed the red wires from the zone valves as they are a separate loop that the thermostats don't connect to. You are correct.... WC-5 is C.
[color=#222222]Hi, I have a honeywell L8148E ([/color][url=https://www.pexuniverse.com/uploads/docs/pdf/hw-60-2278-installation.pdf]https://www.pexuniverse.com/uploads/docs/pdf/hw-60-2278-installation.pdf[/url][color=#222222]) relay on my furnace and am trying to add a new (2020) Google Nest thermostat. I can find any install guides on line that match my wires, since they are labeled as "TV" and "T".[/color]
[img]https://cimg1.ibsrv.net/gimg/www.doityourselft.com-vbulletin/523x640/honeywell_l8141e_aquastats_de7bd24fed7bcc80c53f86f1cfc813f838473202.jpg[/img]
There are two wires connected to "TV" and "T", which ran to my old mercury thermostat. Here is the new Nest with the old wire.
[img]https://cimg1.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/img_20201216_225908667_3d02de6e41b5704b24f72e71f7a63d1564fc20dd.jpg[/img]
[i]Old wire with new Nest thermostat. Connection options are: Y, C, W, and G, R, *OB. [/i]
I have some functionality, but I can tell there isn't enough power to handle all the Nest's features.
[color=#222222]I've read that a C wire could be added by using a 24 external transformer. I see quite a few of these ([/color][url=https://www.amazon.com/Transformer-Thermostat-Competible-Versions-Honeywell/dp/B07DJ7RHS5/ref=sr_1_6?dchild=1&keywords=24v+transformer&qid=1608178176&sr=8-6]https://www.amazon.com/Transformer-Thermostat-Competible-Versions-Honeywell/dp/B07DJ7RHS5/ref=sr_1_6?dchild=1&keywords=24v+transformer&qid=1608178176&sr=8-6[/url][color=#222222]) for sale on Amazon for $20 or less.[/color]
[color=#222222]How would I connect this 24V transformer and my two wires running from the furnace to the nest? Or do I have another solution if I switch out the cable for a 5-wire and connect it in another way to my Aquastat.[/color]
Thanks,
Michael
I've had the nest thermostat for a year now and haven't had a good experience. I have an oil burner with a two wire system and was assured by a nest rep that the Nest would work no problem with this setup. I ran a red white and common from my peerless boiler (replacing the 2 wire from the old boiler with the new 3 wire to the nest. The aquastat also ties in at these terminals as well with a red and white wire.) Since I've had it I get E74 errors randomly. The thermostat heats up the house and then shuts off. It says under equipment detected no power to Rh. After troubleshooting with a Nest rep today he determined either I need to purchase an isolation relay if I'm doing it myself (which I intend to if thats what is needed) or contact a Nest Pro. The purpose of the isolation relay is to communicate an analog boiler to a digital thermostat.
I'm just confused bc im hearing different answers. One will tell me i need the isolation relay. Another will tell me the Taco board (Sr501-4) on the oil burner is capable of doing what the isolation relay would do. Im also confused about the wiring diagram. I have plenty of experience with outlets and lights but transformers and relays are not my specialty so any help is appreciated. Ive attached pictures of the Taco board, the relay I purchased and its diagram.
[img]https://cimg1.ibsrv.net/gimg/www.doityourselft.com-vbulletin/483x256/aub1_f79b32c18d5481538833b640a239cf861f1e83fb.jpg[/img]
[img]https://cimg3.ibsrv.net/gimg/www.doityourselft.com-vbulletin/326x546/aub2_657aedd0b5710502e3640a399e8f4eca3d5ca678.jpg[/img]
[img]https://cimg6.ibsrv.net/gimg/www.doityourselft.com-vbulletin/868x579/aub3_b1f52bd3500128d0334e70ce1849f0b17c7e0ba4.jpg[/img]
12-18-20, 10:44 PM
