My house has fine water pressure for cold water and weak water pressure on the hot water side. This is consistent at all outlets. I suffered with this problem for years and finally got frustrated and tore things apart to see if I could locate the problem. (Turn off the electric to your tank.)

The problem turned out to be that there was a 'clog' at the hot water tank inlet. Inside of the threaded inlet is a plastic insert that 'reduces' the pipe size from 3/4" to 1/2". This plastic insert 'caught' something (pebble? I don't know what) that I dislodged (pushed into the hot water tank) with a screw driver. I then pried up and removed the insert so that it would not catch anything else in the future.

I installed this tank many years ago myself. If memory serves me right this insert was provided by the manufacturer as a method of equalizing pressure between the cold and hot water sides of the system. My main is 3/4" and the cold water takes off from it with 1/2" piping. The main also enters the top of the hot water tank at 3/4" and leaves the hot water tank at 3/4", but at this tank discharge end it is immediately reduced to 1/2". So both the hot and cold water plumbing are ultimately 1/2" throughout the remainder of the house. The tank manufacturer evidently thought it better for the tank (why I do not know) that if the hot water was to be reduced, that it was preferable for it to be reduced at the tank inlet end.

What may work well for the tank screwed up my whole hot water system
When this pipe constriction caught debris and clogged up!

As I said, I cleared the clog by punching through it with a screwdriver. That material fell to the bottom of the tank. I attached a garden hose to the outlet at the bottom of the hot water tank and stretched it to the basement drain. Then I emptied the tank (reminder: turn electric off to tank). Then I opened up the main and flushed the tank. I hope the debris is gone. I hear doing this extends the life of the tank anyway.

Put her all back together and it now works fine! I now have great water pressure all over the house. I then treated myself to a new shower nozzle -one that pulses or sprays or mists and combinations thereof - and am enjoying being the hero of the household!

Great. Likely that plastic insert was part of a dielectric union. Everybody knows that connecting copper pipes directly to a steel tank causes corrosion. However Tom reports that the tanks and pipes don't know it. Sounds like it is like the dogs not reading what the experts in the books say about dogs.

Did the inlet have a plastic tube that went down to the bottom of the tank? The plan is for the incoming cold water to go to the bottom of the tank to be heated, pushing the hot water to the top and out. Otherwise, the incoming water comes right back out the outlet. Great. Likely that plastic insert was part of a dielectric union.