Hi CB2024,
Thank you for reaching out to the Google Nest Community team! I'm sorry to hear about the inconvenience you're facing trying to turn off Eco Mode permanently. I will do my best to help you find a solution.
Since you want the temperature to stay cool, I need to cover every scenario, depending on your case. You can see the following steps based on your model if you have the Nest Thermostat, Nest Learning Thermostat and Nest Thermostat E. You can also adjust this feature on the Nest app or even on the Thermostat display.
There, you can adjust the settings of the Eco Mode feature as you prefer.
Please feel free to let me know once you're done.
Best Regards,
Jonathan
