Nest Power Connector issue

[atranger]

Nest power connector wired to a Honeywell v8043f1051 zone valve as pictured below. Wiring schematic shows the three terminals on the bottom as TH/TR (wired to red) TH (wired to white) and TR (wired to C on the power connector). Multimeter shows 26.8 v between TH/TR (wired to red) and TR (wired to C on the power connector). As wired, the thermostat kicks the boiler on and off so I assume red and white are working as they should. 

the Nest is still throwing a N260 code and the power connector is not detected…am I missing something?

[atranger]

Also…the zone valve is in a really awkward place to get to because of subsequent installation of ductwork for air conditioning so it was easier to cut the thermostat wired and connect the power connector W and R wires to the existing thermostat wires already connected to TR/TH and TH. I assume that’s okay since it turns the boiler on and off in the configuration. See photo

[atranger]

Would it work to just run a wire from the TR terminal to C on the Nest?

[Houptee]

You could probably take the C wire device off and run a C wire directly from Tr as Common.

Is there another transformer in this system that runs power thru the End switches wiring to fire the boiler when the zone valves close?

[atranger]

There is a separate transformer…wondering about either running the C wire from the power connector there, or directly from the transformer to the Nest - more difficult since I need to snake it to the t/stat.

Also…there appears to be two additional  thermostats on the first floor - one heat only and one heat/cool that we’ve typically only used on cool for central AC. One is spliced into the line going to the Nest and one is directly wired into the zone valve. I can’t think of why that would cause a problem, but they’re there.

[Houptee]

The 2nd transformer is usually dedicated to the gas valve and it only runs power thru the End Switch on the zone valve, so it waits for the zone valve to open which closes the switch allows power to pass thru to the gas valve or circulator pump relay.

The separate thermostat for the AC probably has its own transformer in the air handler dedicated just for the AC so you could eliminate that AC T-stat but you would need to connect the Rc (cooling) and the Rh (heating) wires to the Nest but do not connect two commons from each only use the common from one transformer.

Actually that might be best way for this system to work is use the AC air handler transformer Rc and Common to the Nest for your power then put the Y and G.   Then only connect the heating system 2 wires Rh and W to the Nest. Take the C device off the zone valve it won't be needed if you get R and C from air handler.

[atranger]

I just bit the bullet and ran new 3 wire cable from the t/stat to the zone controller and got rid of the power connector…all works as it should.

thanks for the advice 

[Houptee]

Great glad you got it working!