Water Heaters - pilot light problems

hi.. im new to this community form and my problem is i have a new hot water heater (rheem) about two months old and my pilot light and buner wont stay lit. i had a plummer install it. he bleed the gas line and it stayed lit for a little while. and now he is out of town. i lit the pilot light my self and it stayed lit for about one shower and the pilot light and buner both goes out again. it seen like if i used the hot water it will go out but if i dont used any water it will stay lit does anyone knows what to check for thanks for the help i like this forms its great.

good evening,

I would point my finger at the gas control valve, aka thermostat. Just one of several things that could cause this. ( water in gas line, flue/draft diverter problem, combustion air etc)
could be a thermal couple but It most likely wouldn't stay lit all if that was the case.
You should have a manufactures warranty and they should send you the new part at no cost. replacing the gas valve is as easy as changing a spark plug.;)