Our water heater works for a few hours then goes out. I restart the pilot light, it works for a while, then goes out. Any thoughts?

Possible bad thermocouple

How old is the water heater? Is it a newer sealed burner design?

The water heater is about 5 years and yes it is a sealed burner. It seems that I light it, it heats up the tank, then the pilot light goes completely out.

There is a screen on the bottom of the tank that is plugged with lint and dust.

Should I buy a can of air and spray it out? Any suggestions on how to clean it.
Thanks

A brush (like a bottle brush) and a vacuum w/ crevice tool is what I use