One of my Learning Thermostats suddenly will not stay charged and I am getting an E4 error message. I have checked the Rh wire connection which is solid. My other Nest thermostats are working, so I don't think I have a problem at the control board. Advice?
I'm so sorry to hear about the issues that you're having and the error message you're receiving, I'm sure it's confusing but I'm happy to help.
I was able to find this article that will help with troubleshooting the power issue that is the E4 error code.
Please let me know if you have any further questions.