On our planter, the last two years when we started out we couldn't get the liquid fertilizer to start flowing.  Couldn't find anything wrong but if we removed the output hose at the pump, we found it to be under pressure like the pump was pumping but the outlet (or somewhere between the pump and the fertilizer opener) was plugged.  After removing it and all the pressure was released (or more like all the starter shot all over us and the anything else in the vicinity) then when we reattached the hose, everything worked fine.

   Is there something in the distributor that could stick closed and block the flow to each row?  This is a John Blue fertilizer pump and J.B. distributor.  The only thing in the line that seems like it could block the flow is the distributor, but I don't know how it works for sure.  Found a diagram on J.B.'s site that shows an exploded diagram of it but I don't know if it's possible for it to stick shut or not.

TIA for any suggestions.

Steve