Intermittent E74

[FK-BK]

I've recently installed 3rd Gen Nest learning thermostats throughout my house and only use them for heating (gas furnace). Four out of the five thermostats seem to be working fine but the one for our master suite (top floor) is intermittently having the e74 error. When this happens, the heating blasts and makes the space unbearably hot.

I've searched previous threads and do not see any obvious solutions. If the rest of the thermostats are fine I don't imagine this one needs a C wire. What else could it be? Help!

[Markjosephp]

Hello FK-BK

I'm sorry for the trouble this may have caused you — let's see what's going on.

It appears that your system is not providing enough or any power to the thermostat or a specific wire (as a result, the thermostat cannot complete a circuit and displays the report). To isolate:

• Which wire connections does it have on its base?
• Do you have a zoning system?
• Are all your Nest Thermostats the same version?
• Please gather the power readouts under technical info on the wiring report page.
• Make sure the thermostat wires are properly stripped and seated in the thermostat base.

I'll look forward to your response.

Best regards,

Mark

[Markjosephp]

Hi there,

I wanted to follow up and see if you are still in need of any help. 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.

Thanks,

Mark

[FK-BK]

Hi. I went through all the potential issues and solutions with a senior tech via chat and was sent a new (refurbished) thermostat. Installed it without a problem but the intermittent power problems persist even with the replacement thermostat.  Calling in an electrician who can hopefully help. 

Still very frustrated. On top of that, the replacement thermostat doesn't click smoothly. Will be sending that back as well. I figured if my CC was charged a hold at full price, I would not have been sent a refurbished unit. Disappointed in that as well.

[Markjosephp]

Hi FK-BK,

I'm sorry if you have to go through this. We'd like you to have a better experience.

It appears that your system may 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 a wiring report). With the help of an expert, I'd suggest installing a C wire or a Nest Power Connector to avoid power issues. Please check out these articles on how they can help:

• Learn about the common or the C wire
• Nest Power Connector

Please let us know if you have any other questions or concerns.

Regards,

Mark

[Jake]

Hey there,

I wanted to check in and see if you are still in need of any help. Please let me know, as I would be happy to assist, and answer any questions you may have.

Best regards,
Jake

[Markjosephp]

Hello FK-BK,

I'm checking in to make sure that you've seen our response. Please let us know if you have any additional questions or concerns before we lock this thread in 24 hours.

Regards,

Mark

[FK-BK]

A wiring/power issue seems to have been resolved but the heat still activates even when the thermostat says it's not heating. 

[Markjosephp]

Hi FK-BK,

Uh oh! I'm sorry to hear the issue still persists. — let's sort this out.

To isolate:

• Check the target temperature. The unexpected heating may have been the result of someone changing the target temperature without realizing it.
• Check if there’s a C wire on the HVAC board that the customer can connect to the thermostat.
  • If there's a wire in the HVAC board's C terminal, put the other end of that specific wire in the thermostat's C terminal and check if the HVAC system's unusual heating or cooling behavior stops.
• Does your heating still run even if the thermostat display is off on its base?
• Could you share a photo of your current thermostat's wiring?

I'll look forward to your response.

Regards,

Mark

[FK-BK]

Resolving this via email or this discussion board seems very inefficient. I will try chat or a call when I have time.

Faizal

[Markjosephp]

Hello Faizal,

I understand that these steps are a little out of the way, but it's a great start to isolate the issue. But no pressure; contacting our team via chat or phone could definitely help you in real time.

Please let us know how it goes.

Regards,

Mark

[Markjosephp]

Hi there,

I'm checking back in — how's it going? Still need our help? Let us know so we can assist you right away.

Thanks,

Mark

[Markjosephp]

Hi FK-BK,

It has been a few days since the last reply, and I am going to lock the thread in 24 hours. If you have any questions, please feel free to create a new post.

Thanks,

Mark