I recently had a client who had a plumbing issue that involved low water pressure but only with the hot water side of the faucets.
This can be a challenge trying to find exactly where the pipe or clog could be, that needs some attention. I checked all the faucets aerators and found minor sediment built up. Cleaned out the aerators and reinstalled them. Since we knew it was the hot water side of all faucets, I then moved to the water heater.
First, I shut off the water to the water heater and removed the supply line that comes out of the water heater (the hot water going into the house) and checked it for any clogging and found that it was clear. Then proceeded to the short nipple that comes out of the heater that the supply line hooks onto.. We found no clogs. The next thing to do is check the cold side at the water heater, (water coming into the water heater to be heated and distributed throughout the house). I used the same approach as I did on the hot side and removed the supply line and then checked the short nipple that goes into the water heater.
I found that at the base of the nipple going into the water heater, was almost sealed shut with a build up of sediment. Next I removed the nipple in thinking that it needed to be replaced. I found out that the nipple was clear and okay. The build up of sediment was at the top of the water heater and this turned into being a dilemma. Normally, you would have to replace the water heater at this point.
I found that if you gently twist and tap a screwdriver into the sediment, it started to break apart. I made sure not to drop any debris into the tank of the heater. This was not easy! Even though I retrieved most of the debris, some did fall in. This could possibly cause some problems down the road but, it was much cheaper than replacing the water heater.
So, lets recap. When you notice low hot water pressure, remove and clean out the aerators on the faucet(s). If that does not work, check the supply lines and other piping at the water heater. This should do the trick. If you need to replace supply lines or nipples, remove them and take them with you to a local supply store and match the ends and lengths correctly. Worst case scenario would be to replace the water heater itself.
Good luck with all your repairs around the home. Remember to ask questions to gain knowledge in any task you are doing.