reading fault code f20

I've been struggling with F20 on and off for a year... Cleaned the drain outlet, cleaned the inlet screens and fished a stray sock out from under the seal by the door. Finally noticed a green package of papers inside the bottom access panel on the side of the washer with a description if all the trouble codes and a wonderful diagnostic test.... Found out my washer was getting plenty of cold water and NO hot water at all on 4 of the 5 times I ran the diagnostic. Swapped out the water inlet valve (found step by step video instructions and how to test the old part for continuity on RepairClinic.com- they even had diagrams and schematics). So much better to be positive I fixed the real problem then guessing and randomly replacing parts!