There are a few contributing factors that could cause any of the TotalBoat Thixo products not to dispense properly. Here are some common problems and solutions:
Ambient temperature and the temperature of the material in the Thixo cartridge are too cold to flow and dispense properly. Warm up the tube to 80-90°F and see if that resolves the issue. TotalBoat Thixo Flex, Thixo Wood 2.0, and Aluminum Boat Leak Sealer may be more susceptible to this issue.
The material may have crystallized in the cartridge: if not stored properly, the epoxy in the cartridge can be susceptible to crystallization, which would make it more difficult to dispense the material properly. With gloves on, feel the disposed material to see if it has tiny particles that feel like grains of sand. The material should otherwise be completely smooth and creamy in consistency. If crystallization is present, warm the cartridge to 120-150°F in a warming chamber, or by putting the cartridge in a plastic bag and put it in a warm water bath. Change out the water as needed to warm all material in the cartridge to this temperature.  Once this has been achieved, the cartridge should be restored to its original consistency and ready for use.
Use an appropriate caulking gun for the cartridge:
TotalBoat Thixo Pro requires the Thixo Pro caulk gun, or a gun that can accept the 450ml cartridge, and has sufficient mechanical advantage to dispense the material.
All other Thixo cartridges should be used with a manual or electric powered caulk gun - DO NOT USE PNEUMATIC CAULK GUNS.
The caulk gun's mechanical advantage should be at least 10:1 or greater for all Thixo roducts, 15:1 or greater is preferred for Thixo Wood 2.0, Thixo Flex, and Aluminum Boat Leak Sealer.
All Thixo products except Thixo Pro require caulk guns that allow the tip/nozzle to be off center to the rest of the cartridge. The internal workings of the cartridge dictate that the tip is slightly off center. Thixo cartridges do not work in caulk guns that only have a small, centered hole for the tip.