I have two nest thermostats and both were working fine. Noticed an e299 code and under the wiring status had no “w” and “c” connections. I found a blown transistor on my taco sr503 zone relay board that was part of the “w” heat control circuit. Now the nest shows the “w” but still says it is missing “c” wire. I know for a fact the “c” is connected to the common side of the transformer. To test I placed a 50 ohm resistor between “R” and “c” and I measure 530mA of current through the circuit. The transformer is a 40va good for 1.7A at 24v. With the 50 ohm resistor I had about 26.5v across the resistor which using ohms law checks out. So the wiring and transformer is fine I am thinking the best must have gotten damaged where internally the “c” pins circuitry is fried.
Am I missing something here? What should I do? Are nests known for power supply failures/problems?
