All fresh water pipes in your home eventually clog. Deposits and debris in the water build up on the inner walls of the pipe until the flow of water slows to trickle. This is normal. All pipes will have to be replaced eventually. You can prolong the life of your pipes using the back pressure trick. Plumbers have used it for ages.
The idea is to make the water in the pipe flow the other way. This generates back pressure. Most often this will dislodge at least some of the buildup in your pipes. Eventually, however, this trick will no longer work, and your pipes will have to be replaced.
1) Turn the water off
1) Begin by turning off the cold water supply at the water heater. This is vitally important, because it removes a source of water pressure that will eliminate the backpressure we are looking for. Do not turn off the main supply. Only turn off the cold water supply to the water heater. This will depressurize the warm water lines.
2) Plug the faucet
Plug the spout of the faucet or shower you are working on. Plumbers typically remove the aerator, place a dime in it, and reinstall it. The dime will block the water flow. If this is not possible you can try a wedging the end of a towel or sponge into the opening. Whatever you do, make sure it won't come lose when you turn the water back on. On showers unscrew the shower head from the hose. Replace the restrictor plate with a dime and reattach the head.
3) Prepare a second faucet
Remove the airator on a different faucet in your home. Preferrably this second faucet is located lower than the faucet that has the pressure problem. The second faucet is the exit point for all sediments in the system. Using a faucet in the basement will put gravity on your side.
4) Create back pressure
Open the cold and warm taps on the faucet you are working on. This effectively links the cold and warm side supply. Water will flow from the warm side into the cold. The spout is blocked. No water can escape; or at least very little.
If you are trying revitalize a shower with a single control knob, set the knob half way between cold and warm. Depending on the model, this will open up about 50% of the cold and 50% of the warm supply. This is the best you can do.
4) Flush the system
Open the warm water tap on the second faucet in your home.
Now the pressure has an opening to escape. Water will flow from the cold side of your problem faucet into the warm side of the same faucet generating backward pressure and flow on the cold side. From there the water will flow to the open tap.
Soon you should see dirty warm water emerging. It will turn cold gradually as the standing warm water in the lines is purged. If that's the case, you are successfully flushing contaminants from the system. If the water runs clear, nothing is getting dislodged. You have done all you can with this method.