A few months ago I wrote up a quick article about titles not correctly updating in Ionic V1 apps (Is your Ionic View title not updating?). Today I've run into another little issue with the header. I was working on a very quick demo for a presentation tonight and had an app with a grand total of two views - a master list and detail.
Everything was working fine, but then I noticed I didn't have a back button when looking at the detail view. As far as I could tell, my code was fine. Here's what I had in the index.html file:
<ion-nav-bar>
<ion-nav-back-button>Back</ion-nav-back-button>
</ion-nav-bar>
<ion-nav-view></ion-nav-view>
And each view was pretty simple as well. You can see the problem in action at this CodePen: http://codepen.io/cfjedimaster/pen/WxpPap. (I apologize for the formatting in the code - I was cutting and pasting rather quickly.)
I brought it up in the Slack chat and Mike Hartington came to the rescue rather quickly. Turns out the fix was... applying a class. Seriously. Even though the header has a class by default, if you don't explicitly specify one, then the back button won't show up. Literally - the fix is just this:
<ion-nav-bar class="bar-royal">
<ion-nav-back-button>Back</ion-nav-back-button>
</ion-nav-bar>
<ion-nav-view></ion-nav-view>
You can see this working in a CodePen Mike made for me: http://codepen.io/mhartington/pen/YWZBdK.
Obviously I think this is - well - bunk (grin) - so I'll filed a bug report for it here: Back button will not show up if you do not specify a class for the nav bar.
And in case you're curious - here is the "Before" picture of this mission-critical Enterprise demo:

And here is the "After" picture:

Archived Comments
In my case the bar shows up, but no arrow.
Best I can suggest is filing a bug report then. Sorry!
If you're using tabs in your ionic application... the back button disappear if you move to a non-tab screen... I'm dealing with that issue at the moment. Seems like the answer will be to set the back button as an anchor.
The back button is there, it's not visible because the color of nav-bar and back button is same(which is white)
Ok. Same result though - it isn't visible so it might as well be not there. ;)
I checked by changing the color of nav bar, it was there..
I'm not disputing you. :) Just saying that to the naked eye, it appears missing, and this is how I fixed it.