Many brewing issues and inconsistencies are solved by cleaning the piston and attempting to brew again. Cleaning the pistons out will ensure that spray holes remain unclogged and no vacuum loss occurs through the inside of the piston. Take care not to lose the small ball bearing inside the piston when disassembling. This ball seals against the internal of the piston to keep air from flowing through and ruining the vacuum below prematurely. If any grounds build up inside the piston, this ball won't seal and will cause vacuum loss.