This morning my husband had plenty of hot water with good pressure and 15 minutes later I tried to shower and there was no water coming from hot tap, in any hot tap in the house. There is water in the water line coming from tank. We have clear pex and I can see the water coming out of the tank. The tank is only 5 years old but in the last year I've thought the thermostat might be going out because the tank wouldn't always heat the water after we used a lot. Turning the temp up helped. But it hasn't kicked on of its own accord. I had to turn the temp all the way up to get it to turn on. Any thoughts on this. I've talked to everyone including a licensed plumber and no one seems to have a clue...

You need to find a better licensed plumber to talk to. Electric or gas water heater? Put a bucket under the heater drain spigot and drain some water, what temp is it?

It is a gas water heater, the kind that vents right outside the house, not an elevated exhaust pipe. It is very loud when it is heating. I drained some water yesterday and it was hot, but the tank hasn't kicked on since and the water is cooler today. The plumber had said that he thought it could either be an air lock or something blocking the water outlet on the tank and for $97/hr he'd be glad to poke around but made NO guarantees. When I drained the water yesterday, there was a lot od sediment in it, but is clear now. It is just so weird that it was fine one minute and then no water at all the next.

Connect a garden hose to that drain spigot, direct it to a waste area and open the valve. Let it drain for 2-3 minutes and then close the valve. Let me know how long it takes for the heater to start heating. Do not close off the supply line to the heater while doing the drain/flush. Call a different plumber, this guy is clueless.