Bosch troubleshooting IT WILL NOT TURN OFF UNLESS YOU TAKE THE BATTERIES OUT, THE SCREEN IS STUCK ON START UP & DOES NOT ALTER, IT WILL NOT READ THE ANGLES AS YOU OPEN THE ARMS

Before calling service technician, open following link for Bosch troubleshooting resources
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

The model and serial number are usually located on label on side or front of unit.
Link above might have your manual where you can read advisories and required maintenance.

If you are not getting error code, then problem could be plumbing related, but this is a shot in the dark, and one of many places to start troubleshooting.
http://waterheatertimer.org/Crossover.html
Error codes are starting points, and a problem on one tankless can have entirely different cause and solution than same error code on another tankless.

Upvote the help.
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Before calling service technician, open following link for troubleshooting resources.
Manual is best place to start, open manual and word search 'troubleshoot'
Bosh also has troubleshoot page for most/some models
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Suggest that you read manual for required maintenance.
Service technician can also give tips and information for keeping your unit working.

You posted under Bosch tankless water heater.
Fixya is ready to assist resourceful do-it-yourselfer, so read information below, and if you are unable to determine what problem is, post another question saying what you've done so far, or contact service technician and when technician arrives, ask that person tricks and tips for maintaining your tankless water heater.

1) Best place to start is troubleshoot section of manual.
Bosch manuals:
http://www.boschhotwater.com/HelpfulResources/BrochuresManuals/tabid/354/Default.aspx

2) Open pdf of typical manual: troubleshoot section page 33.
http://www.boschhotwater.com/Portals/7/TechManuals/2400E_English_12_2007.pdf
http://www.boschhotwater.com/Portals/7/TechManuals/250SX_English.pdf

3) BOSCH error codes
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/2400ESTechSupport/Troubleshooting/tabid/1295/Default.aspx

4) Bosch has online tech support form:
http://forms.boschhotwater.com/Home/BoschTechSupportForm/tabid/614/Default.aspx

5) Bosch problems at Fixya:
http://www.fixya.com/support/p949576-bosch_1600h_lp_liquid_propane_aquastar_a/solutions

6) Read manual cover to cover and make sure maintenance is scheduled.
For example de-liming is recommended each year.
Utube search de-lime tankless water heater

7) Install DIY tank-type gas water heater and avoid the whole headache
http://waterheatertimer.org/How-to-install-gas-water-heater.html
http://waterheatertimer.org/pro-n-con.html

Add a comment for more free help.
Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Open following link for Bosch tankless troubleshooting resources, including Bosch contact number and link for finding service technician, etc.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Read manual cover to cover, make sure tankless receives yearly maintenance as outline in manual.

Add a comment with your experience so others with same-similar problem can benefit.

Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Open following link for Bosch tankless troubleshooting resources, including Bosch contact information, typical manuals, error codes, tech support, parts, fuel-saver calculator, service bulletins, water heater forum, fixya links, disclaimers, and links for finding service technician.
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Read manual cover to cover, make sure tankless receives yearly maintenance as outline in manual.

Add a comment with your experience so others with same-similar problem can benefit.

Also take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

The screen may be too dim to read. Sometimes when the batteries are low, the screen automatically dims itself. The problem is, it doesn't undo that when the batteries are replaced. Try pressing 2ND->Up arrow key repeatedly while the calculator is turned on and the screen should start to darken so that you can read it.

Open following links for Bosch and Rheem troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Try one of these two fixes, if they dont work for you follow the link below for further troubleshooting.

http://camerarepair.blogspot.com/2007/12/fixing-lens-error-on-digital-camera.html

Fix #1: Remove the batteries from the camera, wait a few minutes. Put a fresh set of batteries back in (preferably rechargeable NiMH 2500mah or better) and turn the camera on. If that didn't work, try pressing and holding the Function or OK button while turning the camera on.
Fix #2: If the camera's batteries ran down completely while the its lens was still open, the camera may show a lens error or not start properly when new batteries are installed. Remove the memory card and keep it removed, then install the new batteries. When you turn the camera on with the card removed it may come back to life, as this triggers a reset in some cameras. Error E30 (for older Canon's) means that you don't have a memory card installed, so turn it off, slip in the SD card and turn it on one last time

I have a Bosch that was stuck in pump down mode even when the door was open.
The problem ended up being too much water in the drip pan below the unit. There is a float in the drip pan that actuates the same limit switch as the internal overfilled float.
I had recently cleaned the incoming water filter and must have loosened the water line tube.

Have you upgraded the software if not try that. Check your battery voltage if it reads around the 2. something voltage then you need to get that battery to its orginal capacity. I dont think you'll get your songs back. Does it have a reset button if so reset it.