I recently upgraded my furnace to a heat pump and installed a new Nest Gen 4 Thermostat. While the transition has been mostly smooth, I encountered an interesting issue with the humidifier. The humidifier would continue running even after the furnace fan had stopped. After some research, I discovered that this is a known bug in the Nest Thermostat software. The humidifier should turn off when the furnace fan stops, but it doesn’t always happen as expected.
To address this, I explored the settings in the Nest Home app. I found that there’s an option to “Turn on humidifier only when heating,” which does shut off the humidifier when the fan stops. However, this feature isn’t clearly visible on all devices, especially the Android app. I had to dig through the settings to find it. If you’re experiencing the same issue, I recommend checking this setting as it might resolve the problem temporarily.
Another workaround I found was manually adjusting the humidity level in the app. By lowering the humidity target, the humidifier turns off immediately. While this isn’t a perfect solution, it gives me some control over the situation. I’m hopeful that Nest will release a firmware update to fix this bug permanently.
In the meantime, I’ve been using these workarounds to manage the humidity in my home. It’s a bit of a hassle, but it’s better than dealing with constant humidity issues. If anyone else has found a more permanent solution, I’d love to hear about it! 
