Bosch 1600h ng will not work after power outage. May have froze or the power draft external systen failed. It was working fine with the power outage but does not work after power came back on.

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

Fix most tankless problems do-it-yourself, same day any brand, for $317
http://waterheatertimer.org/How-to-install-gas-water-heater.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.

1) Call service technician, and when that person arrives, ask about tips and tricks for maintaining tankless water heater.

2) Open following link for basic troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

3) Add a comment with your experience so others with same problem will benefit.

4) 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, but does not take place of service call since you will be doing the work yourself, on a complicated appliance that is affected by perfect cooperation of internal parts, and external factors.

Problem could be air supply, gas supply, venting, part failure or combination of listed things.

Best place to start is manual.
http://www.boschhotwater.com/BoschModel1600H/FeaturesandSpecs/tabid/1024/Default.aspx

Typical 1600 manual shows troubleshoot starting page 19
http://www.boschhotwater.com/Portals/7/TechManuals/1600H_English_0606.pdf

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

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

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.

Possible flow sensor issue. Check to see if your water pressure fluctuates a lot or is fairly steady. These units are sensitive to the pressure. take care.

The incorporation of an anti-back flow, flue pipe insert may be your solution, also the pilot flame control may need to be adjusted up a little.

Good luck
Aduz

I found that the solution to my issue of not igniting was due to a bad pilot electrovalve part #8708501249. It was about a $50 part that was bad from the start.
Really disappointing that Bosch's QA would let a such a defective part ship. I spent about 3 years of using a workaround with a fan blowing air to get ignition until it finally failed. I had a tech look over the system to point me in the right direction.

Aquastar 1600H NG Natural Gas Tankless Water Heater Bosch AquaStar Model 1600H NG Natural Gas Whole house tankless gas water heater, 117,000 Btu input, natural draft with hydro-generated ignition. Provides endless hot water for one major application at a time . Can replace 40-gallon storage tank water heater. Optional Accessory: Model AQ1- Power vent with built-in... More freeze protection when venting horizontally. Capacity: 1 to 2 Bathrooms Dimensions: 8.75D x 18.25 W x 29.75H Weight: 40 Max GPM @ 45F Rise: 4.2 Energy Factor: NG .80 LP .84 Minimum Input: 28,000 Maximum Input: 117,000 Vent Size: 5 Gas Connection: 3/4 Water Connections: 1/2 Warranty: 12-year warranty on heat exchanger, 2-year on parts Features: Endless hot water Can save up to 50% off utility costs annually Perfect for one major application at a time No standing pilot, hydro generated

I hope this helps!
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/1600HTechSupport/Troubleshoot/tabid/1094/Default.aspx
Copy and paste to google search engine!

it sounds to me like the dip tube has failed. this is a plastic tube that is inside the water heater on the cold side. It is designed to put the incoming cold water at the bottem of the tank allowing heated water out at the top. when this tube deteriorates the cold water mixes at the top of the tank instead of the bottom. a new dip tube is about 5 bucks but must be inserted on the cold side by someone with plumbing experience.