I was not able to load firmware 2.1.4 on OS hw v2.1 with the Apr 26, 2015 firmware updater from here: <https://opensprinkler.freshdesk.com/support/solutions/articles/5000381694-update-opensprinkler-firmware-with-downloads->. I tried both openSuSE linux 13.2 and Windows 8.1, and neither worked uploading the firmware. They just seemed to sit there forever, doing nothing. I previously loaded 2.1.3 firmware using Windows 8.1 (with the last loader I suppose), so I know it used to work for me.
However “avrdude -c usbasp -F -p m644p -U flash:w:firmware2.1.4.hex” on linux did work for me to load the 2.1.4 firmware.