Do you have a glue gun fault light on your glue melter and the glue applicator head will not advance to the programmed set temperature?
First, switch the applicator head to a different channel and verify that the issue stays with the applicator. If the issue does follow the applicator, you probably need to replace the heater cartridge inside the applicator block.
If your applicator head is not heating at all, you could have a failed heater or failed RTD sensor. Either one is easy to replace and much less expensive than replacing the complete glue applicator head.
Remove 4 allen screws to remove the plate.
If the RTD needs replacing, remove the RTD cartridge (far left in picture and cut the leads. Splice the new RTD leads and screw on the ceramic wire nuts. These come in the RTD kit. KNRTD83
Insert new RTD cartridge in the RTD bore hole. Verify that all wires are inside the block and will not be pinched by the plate. Install plate with 4 allen screws.
If the heater needs replacing, remove the heater cartridge and remove the leads from the ceramic wire nuts. Insert new heater in the bored hole for the cartridge. Screw the ceramic wire nuts onto the new heater leads and place in the manifold where the wires will not be pinched by the plate.
Re-install the plate with 4 allen screws.
Let me know if you need further instructions.