When I turn on the hot water to my showers--one up stairs and one down stairs--i get how water. When I turn on hot water to any sink in house I get NO hot water, only cold water. Totally puzzled. Have only one hot water heater for whole house.

When I turn on hot water to any sink in house
Just to make things clear are you telling us you have hot water to your showers but no hot water to any of your lavatories or the kitchen sink? Is that correct? Back to you. Tom