How do I turn it on? I press the "on" button and

Clean the arrestor screen located on bottom of heater
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html
http://waterheatertimer.org/images/American-debris-filter-300.jpg
http://waterheatertimer.org/images/Flame-trap-inspection-325.jpg

Check if flam is burning clear crisp blue or lazy yellow
Check the draft
http://hometips.me/Mar/Bosch_Checking_the_draft.pdf

Gene

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

F51 error code is a motor rotor position sensor failure or a lower harness problem. You need to check the motor in manual test mode, not automatic test mode. This will check the hall sensors and do a spin test: Be sure the washer is in standby mode (plugged in with all indicators off; or with only the Clothes Clean or Done indicator on). Select any one button (except POWER, START, STOP, and PAUSE/CANCEL) and follow the steps below, using the same button: Press/hold 3 seconds. Release for 3 seconds. Press/hold 3 seconds. Release for 3 seconds. Press/hold 3 seconds.

If this test mode has been entered successfully, all indicators on the console are illuminated for 5 seconds with 88 showing in the Estimated Time Remaining two-digit display. During the 5 second wait time with 88 showing in the display, press the same button once. You should be in manual test mode. If the button is not pressed within 5 seconds, the automatic test mode begins. The Rotor Position Sensor uses Wash, Rinse, and Spin indicators to detect the three hall sensors. Console can have up to two of these indicators on at the same time when the tub is not moving. Open the lid and rotate the basket by hand. The Wash, Rinse, and Spin indicators should toggle on and off according to the direction the tub is being turned.

SPIN TEST: Make sure lid is down. Press and release: 2nd RINSE or EXTRA RINSE. The lid locks and the lid lock indicator turns on. Press and release; SPIN SPEED, WATER LEVEL, or LOAD SIZE. The motor/basket spins at 23 rpm. Press again, motor /basket spins at 530 rpm. Press again, motor/basket spins at 950 rpm. Press again and motor turns off.

From:
http://www.applianceblog.com/mainforums/threads/32879-Whirlpool-Cabrio-UL-F51-Error-Codes

Thermostat is likley problem , or limit switch control they regulate temp.

I know this is late, but I just went through this problem right now, or rather just a few minutes ago, after finishing the installation.

What worked was holding the up and down arrows together, this is usually what resets other electronics. Well, it worked. It caused the unit to reset and everything started working properly.

Again, while I know this is a late answer for you, I hope it helps others that were looking for a solution and could not find one, like myself tonight.

could be air presure switch which tells pcb that fan is working and would then bring inn ignition system then main gas valve.Would suggest getting gas engineer in.pommie engineer

Call service technician.
Call Boch Phone: 608/257-2225
http://www.bockwaterheaters.com/technical/engineering.html

I don't see a service manual posted on internet.
Without a service manual showing ohm-readings for testing different parts, you are left guessing which part is problem.
Most water heater manuals today recommend yearly service to catch up on most causes for failure including air in fuel line, dirty or corroded burner parts, defective sensor, loose connection, etc.

I'm not quite sure I understand what you have done but, make sure your compresor(outside is running and, that you don't have the thermostat set to "fan". You want the display to show "cool" and then adjust your temp. It sounds like you have the system set to fan and not cool. Provide me with a model number and I will see about getting you a manual.

Try turning the thermostat uo a small amount and see if this makes a difference. I suspect the control board is bad but I would try adjusting t-stat before I spent money on board or service call. Thank you

Yes dothis with the power on ,If it kicks rightbback open then try to find cause befofe trying agaim. Thanks

check the error codes on it by pressing the on off button for 2 seconds then while holding the on/off button press the up button this should display the last 9 error codes let me know what they are