If the volumetric dosing is not working, allowing the shot to run endlessly and the machine is giving the flowmeter error when pulling a shot (when using one the cup button the first three numeric lights flash, when using two cup button the last three numeric lights flash) then the on / off switch for the programmable timer is likely in the wrong position.
To fix this remove the top panel by removing the phillips screw from the circular hole in the top panel and make sure this switch is in the off position. If you are using the programmable on / off timer for the A53 then this does not apply.
If it is in the on position it needs to be changed to the off position. You will also need to unplug the machine and plug it back in after a few seconds to reset the computer so that it knows it is in the off position.