Hi Annette,
I have heard of this problem and all the answers to date could be your 
problem. I would like to add one more scenario. If one is using the slides 
with the red paint box, we have heard that during the summer months the heat 
can affect this paint border and create a wall that will not allow the mixer 
to push the solutions down past the control. We use super frost plus slides 
and whenever we have the problem you are describing it is usually the vortex 
mixer. Hope this helps. Happy Friday All!



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