Dual zone boiler, power connector & external power supply

[E-man]

I've been doing a lot of reading and studying diagrams, and I've figured out what I need to use Nest thermostat on my dual zone boiler with no C terminal on the controller board. (Yes, I know there's a C side, but no way to use it without soldering or taking apart the controller. Neither of which I'd like to do. )

If I got it right, I'll need 2 Nest power connectors. One for each zone. And an external 24VAC power supply. 

My question is: do I need 1 or 2 24VAC supplies? Can I get away with 1, wiring R and C from both thermostats together with the power supply or do I need 2 power supplies? 

All insights will be much appreciated. 

Scott 

[Jake]

Hey E-man,

Sorry for the late reply. I wanted to follow up and ensure you are good to go. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further. 

Best regards,
Jake

[E-man]

I appreciate your reply. Good to go, mostly. After much searching I discovered the R and W wires were reversed on the Argo board. The board only has 2 terminals for each zone marked T1. Reversed them and the Nest started working better.

Also learned the top right lead of the transformer is where the Cwire should attach. So I soldered a wire to that and tied it into the C wires from the ‘stats.

Everything worked well for a day or so, then no heat. It appears everything works except the auto damper is stuck open and the gas does not ignite, only have a pilot.

I'm thinking thermocouple, but that’s above my pay grade. HVAC is coming out in 2 weeks to troubleshoot. Can’t imagine Nest has anything to do with the issue at this point though. Hope it’s just a coincidence.

Cheers!

Scott

[Jake]

Hey E-man,

Glad you were able to isolate what could be the issue. Does not sound like the most ideal time, but I'm sure the HVAC pro will be able to get you up and running. Best of luck, and please feel free to reach back out any time you have any questions. At this time, I am going to lock the thread. If you still are having issues in a couple of weeks, please feel free to create a new post. 

Best regards,

Jake