With the introduction of Windows 10, there was a new feature added that might drive you nuts. “Let Windows Manage Your Default Printer” – This feature will automatically change your default printer to the last one used. If you only have one printer, it really does not matter; but if you have multiple printers it could create more time choosing printers than you need to.
This is switched on by default so if your printer default printer keeps changing on you, which is driving you up the wall simply turn it off.
Click your windows key or the windows icon (bottom left of taskbar), choose the settings/gear icon and then devices. Down at the bottom below your listed printers, you will find the option to turn it off or on. Make your choice and close the window, you can turn it back on by repeating the same steps.
Here is a screen shot of that window.