Nest Gen 3 thermostat and Navien NHB-150H

[tomotvos]

I am revisiting this topic because I am having similar issues with the Nest throwing E102 errors when hooked up to the Navien boiler. I have purchased the Google Power Connector and did the naive thing by simply hooking up the GPC to R/W on the controller board, and the C jack (that was currently unwired) on the same block as R/W on the controller.

The net effect of this is that the Navien would no longer boot up, because it was saying the low-water cutoff was preventing startup. Indeed, the LWC is also hooked up along the same series of connector blocks as the thermostat on the controller, so my guess is that by using the common C, it is somehow signalling the LWC because of the circuitry in the NPC.

So the question is: what "C" should I hook the NPC to on the Navien, for those that have successfully done this (like @Wayupnorthguy ), or do I absolutely need a separate 24v transformer as suggested in that other thread (by @CoolingWizard )?

[luciaaa]

Hi, @tomotvos,

Thank you for reaching out to the community. I'm sorry to hear you're receiving the E102 error code after installing the Nest Power Connector. I'll do my best to help!

I appreciate you taking the time to install the Nest Power Connector. 

The E102 error indicates an overcurrent in the W1 terminal, meaning your system is supplying more power than necessary to the thermostat. This can prevent the heater from turning on. This issue can occur for two reasons: either a wire is installed in the wrong terminal, or the system is supplying too much voltage to that terminal, potentially due to an incorrectly installed power connector.

To ensure the safety and optimal performance of your system, I strongly recommend having a  Nest pro technician inspect your Nest Power Connector installation. An improper connection could potentially damage both the thermostat and your HVAC system.

Let me know if you have more questions.

Best regards,

Ana