Why I Must Type Password Every Time To Reconnect To Home Wi-Fi Hotspot
Here is the solution which worked for my rooted Nexus 5 (Android 5.0.1)

make a backup of wpa_suppliciant.conf file and DHCP folder. Just in case.


Copy wpa_suppliciant.conf file from /data/misc/wifi/ to your PC
Open with any text editor (I used wordpad) and delete all entries with you problematic wifi name on it.
Choose one of the Wifi in the list which you remember has worked before and change SSID and passkey according to you router. Press SAVE.
Copy/replace this modified file into /data/misc/wifi
Delete DHCP folder in /data/misc/
Reboot your phone.
Your phone should now connect to your new wifi :)