WH has worked fine for 7 hrs. Now when the faucet or shower is turn on there is no hot water pressure in the line (incoming cold water pressure line is ok). Since there is no pressure, no hot water because the tank doesn't get enough cold water in to kick in. Removed the plug that reads filter on the side of WH where the cold water comes in. Ran the cold water without it and then plugged it back. WH fired up and ran for 3 days; then started to loose pressure again. Went back and loosen up the filter plug (did not remove it this time and left it a little less tight) and the WH fired up once again...doesn't seem to make sense but it works!!! Any ideas? And what kind of preventive maintenance is recommended for these units in general.