New Reznor EUH-10 and 3rd gen Nest

[matt184]

I have a brand new Reznor EUH-10 electric unit heater, 10kW in my garage.  New 24 volt thermostat wiring.

I’m trying to hook up a spare 3rd gen Nest thermostat.   Heater has 24 volt strip on the back, and I’ve connected wires G, W1, C and Rh.  I reset the thermostat and went through a new setup.

Fan on the heater runs for about 20 seconds, then I get error code e102 for wire W1.

Based on the Nest troubleshooting guides, I’ve come to the conclusion that the Nest is not compatible with the heater, unless someone here has a suggestion?

[Eitanros]

Hello @matt184, 

Thanks for reaching out to the community. I understand you're encountering an E102 error code on your Nest thermostat (3rd generation) after installation. I'm here to help!

The E102 error indicates an overcurrent in the W1 terminal, which could prevent your heater from turning on. This usually happens when the internal breaker in the Nest thermostat base trips repeatedly. While we can't pinpoint the exact cause without inspecting your system, it's possible that the electrical fluctuations causing the breaker to trip are normal for your HVAC system. The internal breaker trips regularly, the Nest thermostat won't be able to reliably control your heating and cooling. In this case, it's likely that your system is incompatible with the Nest thermostat.

For your safety and to avoid potential damage to your system, I strongly recommend having a Nest Pro technician inspect your thermostat and HVAC installation. They can assess the situation and advise on the best course of action.

Let me know if you have more questions.

Best regards, 

Eitan 

[matt184]

Hi Eitan,

Thanks for your response.  I put a voltmeter  on the C and W1 terminals on the heater when the Nest is connected.  When the fan powers on, the voltage starts out at 24, but then drops to zero and then bounces between 5 and 7 until the nest throws the e102 error.

When I put the voltmeter on W1 and R terminals and run the same test, I get a constant 24 volts.

I would expect the C terminal to provide a constant 24v just like the R terminal.

Any thoughts?

Matt

[Eitanros]

Hello @matt184, 

Thank you for the follow-up information!

This error indicates that the internal breaker in the Nest thermostat base has been triggered at least 10 times. Since we can't identify a specific problem with your HVAC system or thermostat wiring, it's possible that the electrical fluctuations causing the breaker to trip are normal for your HVAC system. However, frequent tripping of the internal breaker prevents the Nest thermostat from reliably controlling your heating and cooling, so we need to rule out compatibility issues with the system.

As HVAC components age, they may begin to wear down, leading to voltage fluctuations or changes in tolerance that can result in compatibility issues that weren’t present before. If your HVAC system is older, it may be worth consulting a technician or a Nest Pro to check it. If the technician determines that your system is functioning properly but the overcurrent error continues, it means an incompatibility between the thermostat and your system has likely developed.

Let me know how it goes. 

Best regards, 

Eitan