why back button spamming

[AC Question]

Hello I'm new to here.
I'm facing with the bad issue that some people faced here. My S5 phone back button has gone out of control even am not pressing it, automatically it pressing itself and continues working. Can u help me to fix this problem?

 

[Tim1954]

Make sure it's clean around the area, take any screen protector off if you have one on it.
You can dial *#0*# to get into service mode and check the digitiser hardware.
Try cache partition wipe if able.
If none of this works, it's time to take it to repair shop...