My brand new Bosch 1200 will ignite the flame but then shoots off.

before you condemn the tank, you may want someone to check the venting, if the condensate trap wasn't installed correctly, or at all then this could very well be the source of your moisture!

Your electronic ignition unit is not rectifying through the gas flame, it is a sensitive piece of equipment and has failed.

Remove the pilot injector from old unit and fit into new unit

Gas water heater?
Copy following link to troubleshoot be gas control valve:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Add comment and describe type and brand of water heater

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Call Bosch
Gas Products Technical Support: 800-642-3111

That model number is only shown at one website, and that model number is not shown at Bosch.
Open following link for Bosch:
http://www.boschwaterheater.com/BoschHotWatercomHome/GasProducts/tabid/331/Default.aspx
Search of Bosch for that model number shows no result.

Some water heaters do not have a pilot light. Instead they use hot surface igniter rod that glows red hot
The igniter rod ignites the gas after solenoid valve opens and gas flows to combustion chamber.
The igniter rod and heat sensor have to be operational, and have to be positioned correctly for ignition to take place.
If igniter rod is not working, or if heat sensor does not detect flame, then gas solenoid valve shuts down and water heater does not heat water.

Before calling service technician, open following links for troubleshoot resources including common error codes, Bosch contact information, link to service manuals, and possible product manual
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/2400ESTechSupport/Troubleshooting/tabid/1295/Default.aspx

Call Bosch 800-642-3111
Multiple error codes can mean PC board failure.
AF might be A9, but not sure.
EA is 'no flame ionization detected with water flow'

1. Verify that all manual gas shut off valves are open.
   
2. Check gas type.
   
3. Reset error code and open a water tap to cycle the heater in an effort to purge air on new installations. Cycling hot water tap on and off multiple times may be necessary. If heater still faults with EA error code, have a licensed gas technician properly purge air out of the gas line leading to the water heater.
   
4. Check three wire connections to ignition group on the lower front of the heat exchanger are secure.
   
5. Check gas pressure.
   
6. Check venting specifications are met. Improper venting may cause premature failure of the flame sensor rod.
   
7. Check that the minimum power fan speed has been adjusted to the proper value.
   
8. Observe inside the viewing window of the heat exchanger when a hot water tap is opened. Sparking should be followed by a steady blue flame. If flame is unstable or yellow with proper gas pressure.

http://www.digelair.net/pdfs/TECHLIT/BOSCH/MANUALS/Bosch-ProTankless_AM.pdf
http://www.bosch-climate.us/files/201009031238250.GWH715ES_English_12.2008.pdf

Above are the manuals required to diagnose and service your error code.

EA: No flame ionization detected with water flow.
Verify that all manual gas shut off valves are open. Check gas type. Reset error code and open a water tap to cycle the heater in an effort to purge air on new installations. Cycling hot water tap on and off multiple times may be necessary. If heater still faults with EA error code, have a licensed gas technician properly purge air out of the gas line leading to the water heater. Check three wire connections to ignition group on the lower front of the heat exchanger are secure. Check gas pressure. Check venting specifications are met. Improper venting may cause premature failure of the flame sensor rod. Check that the minimum power fan speed has been adjusted to the proper value. Observe inside the viewing window of the heat exchanger when a hot water tap is opened. Sparking should be followed by a steady blue flame. If flame is unstable or yellow with proper gas pressure.

Consult your owners manual.
http://www.bosch.com.au/content/language1/downloads/70R_UserManual1023.pdf
Heres a new one if you don't have or lost yours. You can't, you got bad advice. tankless system don't have a running pilot light. They operate by detecting water flow and then turning on. Many also state on the lighting instructions to NEVER try and manually light the pilot. Try Bosch tech support. Lowes sells Bosch heaters and they might be able to help you get the support number faster. Hope this helps but please don't go sticking a flame inside there.

I am not aquainted with the Bosch..... But it is a heater. I am going from past experience with gas furnaces and how the process works..... You said that you can get the pilot to stay on if you unhook the Main Gas Valve wire. Do you have 24 Volt power on that wire to Common? Does this have a Flame Sensor? Maybe it got damaged. Does it have a good ground from the burner to the ignition control module? Does that wire to the electro valve go into a plug that plugs into the ignition control.... Maybe that pin is not making contact to the board. Hope this helps If no one else answer right away repost Or call and see if you can get Tech support from Bosch..... I know how frustrating it is you buy something brand new and it doesn't work

Thermo coupler may be defective. it controls the main gas valve by closing main if pilot is out. make sure thermo coupler bulb is positioned over and near tip of pilot flame, but not in the flame. Thermo couplers are inexpensive and easy to change out.