I had a new hot water heater installed and now the upstairs hot water pressure is very poor. Cold water pressure is fine. House is 8 years old. What can I do to fix this myself, if possible, anything simple?

It is possible that some trash broke loose in the hot water pipe and has lodged somewhere in the line. Especially if it is all of the faucets upstairs.

First you need to take the aerators off the spout of each faucet that has one and wash it out, at the same time run some hot water to wash out the pipe in case some is still in the pipe.

At the shower you can take the shower head apart and clean it the same as the aerators, and run hot water.

Now the second thing is a little harder. At the top of the water heater turn the cold water inlet off. No open one of the downstairs hot water faucets, it should drain and then stop running. Now go upstairs and take off one of the aerators, insert a penny in the aerator under the small rubber ring and screw it back in place, now turn on the hot water at that faucet, now turn on the cold water also at that faucet. What this should do is send cold water out of the cold water pipe into the faucet and over to the hot water pipe and down to the faucet that you opened the hot water side downstairs, hopefully this pressure will wash any debris out the faucet downstairs and solve your problem.

Let me know if this helps, it is just something to try.

Letmetellu, You never fail to amaze me.
First you need to take the aerators off the spout of each faucet that has one and wash it out, He has already stated that the cold water was fine. That should tell you the aerators are clear.

Now the second thing is a little harder. At the top of the water heater turn the cold water inlet off. No open one of the downstairs hot water faucets, it should drain and then stop running. Now go upstairs and take off one of the aerators, insert a penny in the aerator under the small rubber ring and screw it back in place, now turn on the hot water at that faucet, now turn on the cold water also at that faucet. What this should do is send cold water out of the cold water pipe into the faucet and over to the hot water pipe and down to the faucet that you opened the hot water side downstairs, hopefully this pressure will wash any debris out the faucet downstairs and solve your problem.
You would take the trash from the second floor and backwash it down into a single faucet? And you've done this before? And it worked? And here all along we've been flushing the wrong way. Remarkable! Tom

You say hot water press upstairs is bad,, what about downstairs? Please let us know exactly which fixtures are affected. You may have a valve somewhere in the hot water feed that will shut off only hot water to upstairs, depending on age and material of valve, the vavle may be plugged. Is most of the hot water piping accesible, or is it all sheetrocked in? Please let us know a little more about this and we will try to help.

Also, I know you are looking for advice on how to fix this yourself, but I really think you would be best to call back the person that installed the new water heater. If it has something to do with a vavle they shut off, or didn't turn back on fully, then it's their responsabilty, however, if it is due to buildup in pipes breaking loose, you may have to pay for the service call. Either way, they should be able to help you out. Good luck and please let us know what you dicide.

Has to be an obstruction in pipe from nearest bath to master.Depending on pipe I would cut pipe way before and way. After the clog and go to work to get it out .a long piece of tubing and some air pressure from an air compressor

Hi Jim and welcome to The Plumbing Page on AMHD.
You piggybacked on a 2 year old dead thread. Before you post look in the upper left hand corner for the date. Thanks, Tom

Great tip! Thanks!