Unless you have a no-button-like smartphone which is a thing nowadays although only a few smartphones have embraced this concept, you cannot a power button not working problem for long. Yes, you can try some methods to fix it in case if it is software related or check whether it is hardware-related. Developers have made it easier for users to use a phone without much use of a power button right from dedicated apps to built-in features and add-ons meant for various tasks, however, it can be used to virtually replace the use of a power button. So, you don’t need to go anywhere if your phone has a broken power button because there is a troubleshooting guide that must keep you well-fed.

How to fix Haier power button not working problem?
Reboot the phone
Hear me out, I know it might sound weird to reboot a phone without a working power button because it is not that possible. The thing is, if the screen is ON, there are a number of ways you can reboot a phone such as you can schedule turn on and turn off that you’ll find within Settings option. Next, you can use ADB and fastboot tools on your desktop to command the phone to reboot itself although you there is a majority of people that don’t know how it works so you should rather ignore it.
Purge all types of cache files
Assuming that phone’s screen is on, you can use it to purge cache files since corrupted files can cause a slew of problems. There are several types of cache files such as storage cache, app cache, and cache partition that you can access within Settings and purge it. This must fix the power button not working problem if it is because of a software issue.
Update all the apps and the firmware
Although it is a long shot but, it is quite possible that an outdated app or firmware is the cause behind power button not working problem. To verify it, you can simply update all the apps installed on your device which is something we simple as you need to visit Google Play Store app >> My apps and games >> Update all. On the other hand, you can update the firmware simply by checking out if you have received an update or not via Settings >> About Device >> Software Updates >> Check for updates. Other possible alternatives are to rollback or install a custom ROM altogether.