Why does this gas water heater keep going out?

Question about a job that just wont quit. Direct vent Apollo gas water heater, getting on about 10 years old, 40 gallon tank. Unit's pilot let keeps going out. Things I have tried:

1) Replaced thermocoupler;
2) Replaced gas valve; and
3) Thoroughly blasted system with compressed air to ensure no blockages, more than once.

Result: The unit turns on and works, for several days, but then it shuts off again. It can be immediately restarted. So it isn't a gas problem, and it isnt an air problem.

Any idea - what gives?

10 year old water heater should not be worked on and definitely not have money spent on it. REPLACE IT! It is past it's life expectancy. Do not waste any more of your time and money on a worn out water heater.

My neighbor used to have that problem. After high winds blowing from a certain direction, the pilot would blow out. A chimney cap fixed that. That being said, and to agree with SHR, I wouldn't spend any more money on a 10 year old heater that is past it's lifespan.
FWIW
YMMV