Homing of A axis from a button

I have built a gantry router machine and I am using a tangential knife on the A axis. After turning the power off and on a few times the A axis starts loosing it's reference. Is there command I can put in the g code file that will rehome the A axis before the program starts? Or can I make a custom button that will rehome? Just need some guidance if it can be done.
Thanks

In the INI file under [JOINT_n] for your A-axis, there is a setting for forced homing: 


Try setting this to "1" and see if that helps.  It should force you to re-home the A-xis if you power off the machine or e-stop (either physically or through software in LCNC)
 

Thanks for the information
I works as you described and I am happy with it.
To home the A axis I have to go to Machine/Homing/Home joint 4. I was hoping to make it a bit easier.
I down loaded Glade and after a few youtube videos I tried to make a A Homing button but I can not see or find a link to my button. Maybe it is there in some other form.
Thanks for your help

I don't know glade, maybe you can repost (or moderators can move this) specifically asking how to create a button in Glade with that function.

I just downloaded Glade into my LinuxCNC Debian 10 machine. I watched a bunch of you tube videos and now trying to produce a button that is linked to Home A axis. I can not find a link for this button. It may be there but I can't see it or maybe there is some other way. I know I can home the axis by going to the drop down menu Machine/Homing/Home joint 4 (A axis) but I would like to make it a bit easier. 
Hope someone can help.
Thanks

Did I get that right, that only the axis selector is missing for your 4th axis and therefore you cannot home it?
Normally that should be possible for all axes. See here the sample configuration for 9 axes:
 
 

But if you still would like to do that with a Glade button, you have to use the function in your button callback function. See linuxcnc.org/docs/2.9/html/config/python...mand_code_attributes for reference and also for an example.

Thanks for the advice. On my axis main page pushing the Home All does home all my axiss (XYYZA) . I installed VOLATILE_HOME = ) in the A axis in the ini file to force me to rehome the A axis after I cycle power. It is nice to know that making a Glade button is possible but this is something I really need some help on.Any guidance would be welcome.
Thanks again
Jan