No hot water, pilot light lights but no burner ignition

possible faulty pressure switch connected to the water line and that is failing to turn on the main gas tap solenoid
best have it checked by an accredited gas fitter or service center for the make

Tankless?... call service technician

Tank? clean arrestor screen, replace gas valve thermostat
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Gene

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

I know from you info that you don't want to work on it any more but this will help if you decide to try again.

Troubleshoot
Q. No Spark At Pilot? Q. Spark Appears When Hot Water Is Turned On, But Pilot And Burners Will Not Ignite? Q. Pilot Sparks Continuously With No Water Running? Q. Pilot Lights But Burners Will Not Come On? Q. Main Burners Go Out During Hot Water Use? Q. Hot Water Temperature Fluctuates At Tap? Q. Water Is Too Hot? Q. Water Is Not Hot Enough? Q. Burners Do Not Burn Cleanly; Yellow Flames When Operating? Q. Burners ignite without water flow? Q. Low hot water pressure? Q. Noise when the heater is running?

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

it sounds like the flame sensor is dirty or faulty. when the pilot lights the flame sensor rod recognises the flame to allow the main gas valve to open and ignite the burners. you can clean the flame sensor with some steel wool or sandcloth

I have the same problem with the same model. The problem has been identified by a friend of mine, correctly, I think.
This is a very dangerous problem involving Bosch's much touted safety feature, ironically enough. IT IS THE FLAME SENSOR IN THE GAS VALVE. The flame sensor is supposed to confirm that the pilot has lighted BEFORE the main gas line sends gas to the main burners, after which the pilot shuts off. The pilot light is not coming on, the sensor that shouldn't let gas fto the main burners is failing and the main gas is flowing and ignighting from the spark that is supposed to light only the pilot in a big explosion.
This is the 2nd unit of this model that has failed. I think Bosch should do a recall

This is a great unit! Try turning the flow nob to the half way point and the flame all the way to low. Run the hot water tap and slowly turn the flame dial until you hear the unit try to light. Every house is different regarding the restrictions in the plumbing and water pressure. Once the unit tries to light that is your minimum setting. It is best to leave it there.

The sensor that allows the pilot to ignite is at fault
replace the probe that points at the pilot light which is the sensor

There should be a thermocoupler, it is that bulb that sits in the pilot flame. If it is not functioning properly the main gas valve will not open.. Hmmm, Is the main valve in the on position?