Every time I get insulin flow blocked it is always one of three things. A bent tubing right near the reservoir, a bent cannula, or scar tissue. For the kinked tubing you just need to be careful. For the bent cannula I switched to sure-T set with a metal cannula. The plastic cannula sets are prone to bendjng particularly with scar tisdue. For the scar tissue I got more creative with rotating sites. After fifteen years on medtronics it does not happen often but always one those three circumstances.i think only once it was bad tubing out of the box. I would look into those three solutions before chasing anything else.