somehow pressurized the up side

Clark,

 

Yes, consider the master relay weakly welded its contactor, too (during ugly arcing 'cause the current just wasn't enough to hold 'er in solidly).   Or, your master relay got screwed up from low voltage.  That is, until heavy duty power was applied.  Whatever.

 

The pump won't run without power.  The problem was electrical, not hydraulic.

 

Anyway, sorry for the damage.  Maybe others will also add the $0.15 diodes for a modicum of prophylaxis.

 

Remember this axiom: It can't ever happen if it can't ever happen.

And its corollary: It can happen if it can happen.

 

(Aside to Lorn - Notice the probabilistic nature of both the axiom and its corollary.)

 

These are deep thoughts, best contemplated over a relaxing cocktail with the ribs working on the bar-b.