Dear M. Neale,
please make sure that you are working like it is written in the current instruction.
You should use about 150-160°C and 90 seconds for the first step and 30 for the second step.
If a line is too thin and you see it is not working, make sure that you are using a thicker line.
Normally we can guarantee perfect results with line thicknesses of 0,5 pt.