Retired plbg1
Did you check the valve on hot water heater, make sure it is open, if it is then turn water off at main valve and take valve on heater apart and check the washer and turn on main valve and see how much water you get, if that is okay then problem is after the heater valve. check all fix. valve for swelled up washers and clean all areaters if it still is bad then call a plumber.
