Unregistered-John Boy

First check and see if the inlet valve to the water heater is open all the way.

Second if you have hard water, chances are the outlet (hot side) is plugged off with the hardness of the water. Turn off the water on the inlet to the water heater. Loosen the union (if there is one) on the hot side. Or you may have to cut the pipe on the hot side and install one. Take a hammer & screwdriver or a drill that will fit inside the pipe and remove the sediment.

After removing the sediment and reconnecting the union open a hot hose bibb (on a laundry sink , or some tap that doesn’t have a screen) Turn on the water valve to the water heater a flush out the sediment. Perhaps you would want to place a pail under the opened tap to see the sediment that you removed. If you open the kitchen sink tap you will have to remove the aerator to get the crap out.

I seen this time after time, plugged-off at the outlet side of a water heater.

John Boy