I recently had my kitchen remodelled in my 60+ yr old house.
In the process, the contractor shut off the water from the basement so that my family had no water on the 1st floor (incl. Kitchen) and the 2nd fl. Bathroom. We were asked to use the bathroom in the basement for the time being, which was a hassle but acceptable.

While he was doing the kitchen wall, he pointed to the pipe hidden in the wall to be the pipe going upstairs. He mentioned that it's a "black pipe" instead of being copper pipe. He then hit the pipe with his wrench a couple of times (as if kicking the tires of an used car) but with enough force that the pipe noticeably shook for a while.

Anyway, when the water was turned back on, we discovered that while the cold water pressure was fine everywhere in the house, the hot water pressure was extremely low as both the kitchen and the bathroom upstairs had only trickling amounts of hot water. The contractor (who never came back to take a look even though he said he would) said that it's not even a problem where I just need to let water trickle for a while and let air out. Contrary to his suggestion, even after hours of letting hot water run, problem still exists. (BTW bathroom in the basement has great pressure both hot and cold)

I asked a local handyman to take a look and he said he needs to tear down the walls just to get to the pipe and that he suspects that the pipes need to be replaced. But because I thought hiring a new plumber to open up walls to replace old pipe to be my last resort, I began doing some research on the web and I wound up here.

After reading some other similar posts, I did check the hot water heater (in the basement)to see if it needed to be drained. My water heater is made by Reliance (model: Sta-Kleen 805) and on the side of it, it boasts its "Self-Cleaning Feature...Never Needs Draining." Should I still TRY to drain the heater?

Help~ Where do I go from here?

Your plumber really did a number on you. By banging on the pipe in your wall he dislodged minerals built up in the pipe wall and the first faucets making a draw sucked it up.
Now your system and faucets are clogged and must be cleaned and flushed
Out.
First remove the aerator from the faucets spouts and check and clean the screens. It may be as simple as that. If that don't get it then the faucets in question will have to be opened up and the seats and inlet ports cleared. Before reassembling the faucets turn the hot waer back on and flush out the supplies. Need more help? I'm as close as a click. Tom

I've been reading a lot of case scenarios about hot water turning lukewarm upstairs which is my problem. There's basically two supplies branching out of my basement gas heather ( year old); one branch is fine. The other goes to laundry' kitchen and upstairs, and I suppose is clogged (is this possible, they are all 1/2" copper pipes' 12 to 15 years old)? We already cut off the exposed portions of the piping in basement and replaced them with 3/4" pipes and did a much better job straightening sharp turns. The cold water has a lot more pressure but still no hot water. My plumber is as puzzled as I. Any suggestions? Can I back pressurized the pipes with air? How can I do that?

C'mom speedball , I need some of your wisdom, please!.