Before calling service technician, open following links for Bosch troubleshoot resources:
1) General resources:http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
2) Sales page: Notice the paradoxical promotion of unlimited hot water that saves 50% off utility bill.http://www.boschhotwater.com/BoschHotWatercomHome/GasProducts/BoschModel1600H/FeaturesandSpecs/tabid/1024/Default.aspx
3) 1600H troubleshooting. Click each item and it opens drop down menu that also has links to service bulletins. Lots of reading, but a great way to get familiar with your product.http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/1600HTechSupport/Troubleshoot/tabid/1094/Default.aspx
I do not recommend tankless for the number of difficult and expensive problems, the required yearly maintenance, plus the specific need for incoming air quality, sufficient quantity of gas, water quality, water pressure, water volume, and correct venting and drainage of vent condensation. And never recommend self-installation since most tankless manufacturers refer immediate problems back to the installer.
Assuming the tankless was installed correctly and not defective:
Other problems can be caused by household conditions.
For example crossover:http://waterheatertimer.org/Crossover.html
Tight house: tankless require more incoming air than tank-type because they burn so much more fuel per minute of operation:http://waterheatertimer.org/pdf/Bosch_Ventilating_tight_houses.pdfhttp://waterheatertimer.org/pdf/Bosch_Overcoming_fluctuating_temps.pdf
Low water pressure:http://waterheatertimer.org/Low-hot-water-pressure.html
Take a moment and vote on answer:
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.