The pressure in the hot water lines throughout my house is less than 50% of the cold water line pressure. The house is nine years old with 3/4" and 1/2" copper supply lines. All faucet filters have been removed and cleaned. The hot water heater has been drained to remove sediment. All valves have been checked to insure they are in the full open position. When I drained the hot water heater to remove sediment the pressure was fine at the drain valve but remained very low at all hot water outlets. The reduction in hot water pressure has been gradual over the last year or two. What do you think could be causing this problem?