Mix 50 g (4 T) of granular citric acid in 2 cups of warm water until dissolved.  This is 10%. 
Note:  Many people use 1 T/4 cups as a maintenance solution – we are doing restorative, hence much stronger, but with very short contact time. You can find citric acid at feed stores, homebrew shops and pharmacies. Dezcal commercial descaler will work as well.

1. Put 10% solution in brewer.
2. With manual release, heat to 150 F.
3. Release water until half is gone – about 30 seconds. (fully clogged units started flowing within about 15 seconds)
4. Shut the valve and wait 30 seconds.
5. Open the valve and allow to fully drain.
6. Solution can be saved for many more uses.
7. Fill reservoir with water.  Again, heat to about 150 and let drain through.  If everything is now working right, release time should be between 2:30 and 3:00 minutes.

You may wish to run a 2nd rinse.