I have three heat zones. There is no zone controller board. Each Nest thermostat (not learning and not E) is currently wired before the zone valves. Each thermostat has two wires going to it. The zone valves do not receive any power unless the Thermostats are on. (I verified this with a multimeter). How do I wire my power connectors to my system? The thermostat is powered by two 24v transformers.
Can I connect the power connector downstream from the Thermostat but before the zone valve?
Which Taco Valve Zone Control do you have installed?
How many wires are going to the thermostats?
Which Nest thermostats do you have?
I have read about using T1 on the valve terminal to supply the C wire connection, but by my understanding of the circuit, T1 only supplies common when the relay is energized, as you have found. I don't have access to a Taco controller, so I could never verify my thoughts as you have.
When I was looking at the circuit for a Zone Valve, it looked like the T2 terminal was connected to common all of the time. Check that out if you can.
If that isn't the case, you will have to use one leg of the 24Vac transformer output as the C terminal, or you can use an external 24Vac transformer and connect it like the following. You will only need one external transformer for all of your power connectors.
Step 6.D is only needed if you use an external 24Vac transformer.
You must create a C wire when using a Google Nest Thermostat with a 2-wire heat-only system. The best way to create one is by using the Google Nest Power Connector and wiring it like the diagram I have attached below.
You will need a separate power connector for each thermostat, and you can connect the C terminal of the power connector to the white wire on the 24Vac transformer.
