hvacthermostatthermostat-c-wire
Can someone please help me find where to connect a C wire for my smart thermostat? Here are some pictures with descriptions. It is difficult to get to the 24v connection in the back. My schematic doesn’t show where the condensate pump would go so I am getting a little confused. A lot of other posts I have seen about this have much simpler setups.
Help would be appreciated.
According to the schematic, the B terminal does appear to be connected to the transformer.
I'd actually trace the wiring in the unit just to confirm, but based on the schematic it looks good.
You'll want to make sure the transformer has enough power to supply the additional load of the new thermostat, but typically it isn't a problem. If you hook up the new thermostat, and the fuse inside the unit blows. That would be an indicator that the thermostat is drawing too much juice.
From the pic, I'm guessing the transformer is the black device under the junction box. Looks yellow and purple coming off of that, you're connecting to the yellow, so the purple would be the common. To be sure, you'd want to connect a multimeter and verify the voltages to ground. It would also be helpful to find the wiring diagram for your boiler to be sure you're interpreting these wires correctly.
Assuming purple is the common, you'd run your wire to that, preferably through that wiring block where the other thermostat wires are connected on the left. There's no issue connecting the common to multiple places.
Best Answer
That wirenut is as good a spot as any
Based on the information posted, I would try tapping the C wire at the wirenut you point out in your photo; it appears to be in the correct place in the circuit, and the wiring diagrams for your unit call out blue for C wires within the unit as well.