After having to hit the button 6 times to get a full cup of coffee (for the last 2 weeks!), here are my two cents worth..... get a small phillips screwdriver, a small flat screwdriver, wire snips, needle nose pliers, 10 small zip ties, some type of small wire poker. THIS EFFORT MAY CAUSE DAMAGE TO YOUR PLASTIC PIECES. Unplug and drain the water. Open the hatch and remove all the screws(4, I recall) holding the lever cover. Remove the cover. Then work very carefully to pry the top back cover from the machine. I was able to get the left side loose pretty easy. The right and back side clips actually broke off of my unit but didnt damage the fit. These were intended as "one way clips" with no option of repairability. I was not too worried about this damage and would rather deal with this than drop another hundred bucks on a new maker.
Flip the unit upside down and pull out the 5 screws holding the bottom on. Make sure not damage the 3 grounding wires attached to this plate. Locate the little pump motor and pull the 2 screws holding the motor. Use your needle nose pliers to squeeze and slide off the small hose clamp holding the accordion hose to the side of the pump motor. Flip the unit back over and clip the big zip tie holding the cluster of hoses below the plastic clip. You are trying to locate the bigger tube that runs down to the pump motor. Once located, clip the zip tie on the bigger tube and clip the similar zip tie on the pump motor and remove the length of tube and check valve. Take this whole thing to the sink and flush out the muck(water and vinegar). Use you wire poker to gently push into the check valve to ensure it is cleaned out and working. Blow into either end of this hose/check valve to make sure you can blow one way but not the other. If you can blow both ways, the valve needs more cleaning and poking.
You will also find a similar check valve under the hatch lever. Cut the zip ties at either end of this unit, remove it and do the same cleaning, flushing and actuating of this valve. The crud that came out of my check valves was pretty bad and was the cause of all my problems.
Reassemble everything you took apart. Make sure to get the zip ties back in place on all the tubes and get the hose clamp back on the accordion hose on the side of the pump. It is easier to feed the bigger tube up through the top of the unit before connecting it to the pump. Zip tie the cluster of tubes back under the black plastic clip. Snap the top back of the unit back in place if the tangs didnt break off and if they did, hold it on with clear tape to cover up the booger marks. Tuck the power cord back into the little horseshoe housing and reinstall the bottom cover with 5 screws.
This is a more advanced home appliance repair but only took me a little over an hour to accomplish. My unit is no longer aesthetically perfect but it made a full cup of coffee on the first and only hit of the button.
PS. I like the "industrial-mechanical" look and may just make a clear plastic cover to reinstall on the top of my maker.