Low pressure or low flow? pressure is pretty consistent in most residential applications...flow however can be effected by scale, mineral build ups etc. These usually occur in "constricted" sites like shower heads and faucet aerators. In many cases descaling with a soak in vinegar with improve the flow.
When you say low water pressure on hot water side. It this at all faucets and tub spouts, or just one faucet in particular?
If its only one faucet, then clean the screen on the discharge spout on the faucet.
If its all the faucets then check the shut off valve on hot water heater first as it may not be opening all the way.
You can also flush it out, but its doubtful that this would cause any real low water issue. Unless some rust floated into the dip tub where the water exits out of the heater and plugged it. Then flushing may help.
The problem was a malfunctioned "check valve" Thanks
A check valve installed between the tank and point of use?....that would be a new one form me.
What is installed on the top of lots of water heaters, and the first I ever heard failing is a little ball check valve that opens when the water is running through the heater. A spring holds it closed when water is not on. Its reason for being there is to stop convection currents from traveling out of the water heater causing it to turn on and off more during periods of none use.
You often see them as blue and pink disks that are fastened right at the heater inlet and outlet where the female coupling is typically installed.
cool...learned some new stuff today
Possible mineral deposits / electrolytic action as dissimilar metals come in contact without the use of a dielectric fitting such as a union or insulated nipple