I have a Bosch GWH 2400 CTD EFS NG tankless water heater. It has been installed on operating for over a year in the last several days it has an error code A3. The first two times I was able to reset it. Now after clearing the fault,the fan starts running w/o burner ignition for about 3 seconds then stops with fault A3.The manual says to check the jumper cables at the top right of the combustion section. They are securely attached. Help! Bill

SOURCE: I have a Bosch GWH

Call qualified service technician, and ask that person questions about maintenance and tips.
Then keep service technician number in rolodex-wallet.

Resourceful do-it-yourselfer will find following links handy.
Tankless are maintenance heavy, and Bosch and Rheem etc say to call service technician for recurring problems. Especially when short-hand troubleshoot section doesn't solve problem.
People spend years learning how to service tankless.

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

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

Bosch manuals:
http://www.boschhotwater.com/HelpfulResources/BrochuresManuals/tabid/354/Default.aspx

Bosch problems at Fixya:
Open following links and read about tankless problems to understand the field and glean useful information.
http://www.fixya.com/support/p949576-bosch_1600h_lp_liquid_propane_aquastar_a/solutions

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

Post question on pro water heater forum: This is where I go to catch up on latest info in always-evolving water heater industry.
http://www.thetankatwaterheaterrescue.com/forums/forum3/

Pay for an answer at fixya:
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.