I tried installing the Nest Thermostat but it says the wiring is incompatible, but upon searching in this community, it seems like others had success with a Honeywell TH4110D1007, so I'm wondering if there is something in my wiring (the letters in the picture) that is tripping this up. It's a relatively new house (2015) so think it would be odd if wiring was such that it wouldn't accomodate a modern thermostat. Thanks so much for all your help!
In the picture it is hard to see the letters for the terminals the wires are connected to. It looks like it is probably something like this:
W - White
Y - Yellow
G - Green
R - Red
Those are relatively normal connections and a Nest thermostat should be compatible. HOWEVER, there is not a C Common wire connected. Nest thermostats work best with a C "common" wire.
Use the Compatibility Checker to see if your Nest model is compatible.
Information about the C (common) wire. Here are some options:
You may not need C, but is it good to plan for it just in case.
If you have the "Nest Thermostat" (opposed to E or Learning) it will not run on batteries alone for any length of time. It requires a source of power. The batteries are primarily used as backup during power outages or when the furnace is being maintained. It may get enough from the other wires, but if not, you would be replacing batteries frequently - possibly every few days.
My recommendation is always use C if at all possible. Given the age of the home there is probably an unused wire in the thermostat cable, and most likely there is a C connection on the furnace.
Read the documentation linked to in my first reply to find out more information.
Thanks @sporfrog for the advice and @Markjosephp for following up. I'm a bit at a loss. There is a spare blue wire in my thermostat that isn't plugged into a slot and I was advised to plug that into 'C' in the thermostat and make a similar connection in my HVAC. Below are the pictures from my HVAC, the blue wire seems to be connected bunched in with the other wires (see below). I'm a little over my skis here, appreciate any advice. TIA!
Thanks so much for the help sporfrog.
I wanted to follow up. If you are in need of a Nest pro, you can follow the link here to learn more about that. Please let me know if you have any questions from here, as I would be happy to take a closer look and assist you further.
I suggest seeking out an HVAC professional. The images attached are not the thermostat cable and should not be altered or changed.
If you are still determined... there should be a cable with multiple wires in the cable. It will have the same outside jacket color - typically a shade of brown - as the cable at the thermostat. Inside it will have multiple wire colors that match those at the thermostat. The suggestion for using an extra blue wire applies to an unused wire in that cable NOT any blue wire in the furnace.
The wires in the thermostat cable will be connected to a wiring terminal typically on or near a circuit board.