You must set the print head resistance value after changing the print head
You can find the resistance value on the print head
Press the Menu Button
Use the down arrow button to scroll down to Set Up Printer and press select
Scroll down to print settings and press select
Scroll down to Head Resistance and press select
Use the up or down arrows to change the print head resistance value to match your new print head (Values are in 50)
Press Done and Save