1) Error code A2 shows on following link:http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/2400ESTechSupport/Troubleshooting/tabid/1295/Default.aspx
2) 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
3) As a general rule, tankless are best when installed by experienced, trained technician.
4) This is partly because Tankless manufactures refer you back to installer when there is a problem, and party because so many factors affect tankless operation.
5) Tankless require perfect alignment of factors to work properly, including vent, air supply, gas supply, combustion maintenance, water flow, water pressure, water quality, overall maintenance, plus internal parts working in harmony.
6) Read manual cover to cover, make sure tankless receives yearly maintenance as outline in manual.
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