My husband just replaced the thermocuple on our water heater but it still won't stay lit, now what?

Baby, what kind and size of water heater? How old is it?

Whirl Pool, 2 years old, 50 gallons

At 2 years old it should still be under warranty, I'd check with whirlpool. Lots of complaints, they might take care of it. Is this a "Flame Lock"?