Suddenly E195 Error with Year-Old Nest Thermostat E

[DaveTheNerd]

I have two zones of forced hot-water, propane-fired heat in this building: a Nest Thermostat E in the office, and a Nest 2nd Gen up in the studio. This morning, the Office's Thermostat E started reporting E195 "No Power to R Wire Detected." 

The Studio's 2nd Gen has no such issues. Both are connected to the same boiler, just different zones. The zones are served by Taco valves (if that's relevant).

Back to the "E" in the Office: It shows that there is Power coming into it on the Diagram, though, and if I remove the wires from the back plate I can see voltage across them. 

Any idea what's going on? Is the "E" more sensitive to, say, a beginning-to-fail transformer than the 2nd Gen is? Or is the valve on this zone starting to fail or something? I was able to get heat to flow by forcing the valve open, so clearly the boiler itself works fine...and the zone in the Studio works fine, too, wireless and everything.

I'd appreciate any thoughts, of course. Thanks!

[Markjosephp]

Hello DaveTheNerd,

Thank you for taking the time in letting us know about your inquiry. Let's see what's going on.

It appears that your system might not provide enough power or any power to either the thermostat or a specific wire (so the thermostat can’t complete a circuit and shows aa report). How's your thermostat? Are you still getting the same report? If so, please try the steps here:

• Gather the power readouts from the thermostat under technical info.
• Make sure the thermostat wires are properly stripped and seated in the thermostat base.
• Turn off the power from the breaker to your HVAC system.
• Remove the C wire and leave it disconnected if there is.
• Check the air filter. A clog in the air filter can limit how much air flows over the cooling coils. If the clog persists, the cooling coils can freeze and cause the system to shut off.

Let us know how it goes.

Thanks,

Mark

[Markjosephp]

Hi there,

I'm checking back in. Were you able to do the steps above? I'd be glad to hear from you — I'd like to make sure everything is working.

Best regards,

Mark

[Markjosephp]

Hi DaveTheNerd,

I just want to check if you have seen my responses posted above. Let us know if you have additional questions, otherwise we'll be locking the thread in 24 hours.

Best regards,

Mark

[DaveTheNerd]

Thanks, @Markjosephp! It turns out the Taco Zone Valve malfunctioned and that was causing this symptom. We replaced the zone valve and all is (now) well again!

[EdwardT]

Hi DaveTheNerd,

Thanks for the update. I'm glad to hear that it's working fine now. Please observe it for now and let us know if anything comes up.

Thanks,

Edward

[EdwardT]

Hi DaveTheNerd,

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do. 

Thanks,

Edward

[EdwardT]

Hi DaveTheNerd,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward