Symptoms
You are using Windows 10 and you have set a specific printer as your default printer in Windows 10 but the default printer changes to other printers once in a while.
Cause
In November 2015 Microsoft released a major upgrade for Windows 10 (Build 1511). This major Windows 10 update introduced a new setting to change the default printer in Windows 10. When turned on, the default printer is the last used printer.
For example:
A Brother 5450DN Laser Printer is your default printer in Windows 10 and for a special case you need to manually select your printer to a different printer driver. With this setting turned on, your default printer in Windows will not be Brother 5450DN Laser Printer anymore but the last used printer.
Change via Printers & Scanner Settings (Recommended)
Go to Settings > Devices > Printers & Scanners
Disable the setting Allow Windows to manage my default printer by un-ticking the box
Then click on the printer you want to be the default printer, select Manage and then select Set as default
Change via Registry
Open the Registry Editor (Right mouse click Windows Start → Run → Regedit)
Navigate to this key: HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows
For name “LegacyDefaultPrinterMode” set the “Value data:” to “1” to return to the old Default printer behaviour in Windows 10
