On this page, you will find more information about the most common causes and most relevant solutions for the Nest error 'E91'. Do you need help straight away? Visit our support page.
The Google documentation indicates that error code 'E91' is caused by the following problem: "E wire without O/B wire".
Do you think there is another cause for this error? Let others know in the comments.
We've created a list of solutions which you can follow if you want to solve this Nest problem yourself. Do you need more help? Visit our support page if you need professional support with Nest right away.