Atwood G6A-8E is GAS only water heater
Uses 12V DC so no circuit breakers.uses FUSES (unless RV MFG used DC Circuit Breakers)
So find/check Supply Fuse for water heater
Check Green Wire connection....Ground Wire
Brown Wire....thermal switch (Clear Tubing). One time fuse that blows at 190*F (exposure to flame blow v=back from combustion chamber)
Remove it and connect Brown Wire to T-stat to test if water heater will turn on/heat water
If it does.....
*Replace thermal fuse
*Clean out combustion/exhaust tube ...run wire up thru combustion and out exhaust =--tie a rag to wire then pull back thru to sweep the tube