Default [Q] Update omni-ROM nightly ver

Hey guys
I'm kind of new around here so here is a quick question
I'm using omni-ROM based on 4.4.2 ver.20140307
Now I've try to update in Settings->about phone->sys update
But all it does is to redirect me to the TWRP Recovery mode and nothing happen
I've heard someone says it's should be automatic; but it's not.
So...I've downloaded new ver 20140410 to SDCARD and try to flash it after dalvik cache wipe; but got a failed error.
Do I need to wipe-factory every time to update between nightly?
Or is there something I do wrong?
Thanks for your help.