When we turn on master bath sink to the hot position only cold water comes out, when we turn the shower to the hot position no water comes out at all... what could be causing this. The rest of the house has plenty of hot water.

Wow, I have the same problem. My tenant called tonight and said one of her bathrooms has no hot water coming out of the sink or shower. There is a kitchen further down the same supply pipe that has no problem. The bath comes off right after the water heater outlet, and there's only a ball valve shutoff before it goes up to the sink/shower. I'm going to figure it out tomorrow, so I'll let you know what I find.

Last night, I turned on both the sink and shower hot water faucets and there was nothing. The kitchen is at the end of the line and runs off the same hot water line and it was fine. I went down to the basement and checked the shutoff valve for the bathroom line and nothing was amiss. This morning, before anything else, I went up and turned on the bathroom faucets and there was hot water... I have 50 gal electric water heaters for each unit. It's a mystery...