Bosche model 45-550301

1) Check for crossover:
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/pdf/No-Error-Code.pdf

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Yes you need to delime tankless each year.
http://waterheatertimer.org/pdf/Bosch_Descaling-heat-exchanger.pdf
http://waterheatertimer.org/pdf/Rheem-De-lime-tankless.pdf

Contact Bosch for exact repair information. My records show following number for tankless gas: 800-642-3111
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

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

Before calling service technician, open following links for Bosch error codes, and contact information, and possible product manual for your model, etc:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Bosch_EA_error_code_troubleshooting.pdf
http://waterheatertimer.org/pdf/Bosch-GWH2400ES-error-codes.pdf
http://waterheatertimer.org/pdf/Bosch_A4-E4_error_code_troubleshooting.pdf

Error code AE is not shown, but error EA means "burner flame not recognized by control unit when water is flowing"

There is also error A3 and A3 E3: jumper connection is not correct

Call Bosch
Gas Products Technical Support: 800-642-3111

That model number is only shown at one website, and that model number is not shown at Bosch.
Open following link for Bosch:
http://www.boschwaterheater.com/BoschHotWatercomHome/GasProducts/tabid/331/Default.aspx
Search of Bosch for that model number shows no result.

Some water heaters do not have a pilot light. Instead they use hot surface igniter rod that glows red hot
The igniter rod ignites the gas after solenoid valve opens and gas flows to combustion chamber.
The igniter rod and heat sensor have to be operational, and have to be positioned correctly for ignition to take place.
If igniter rod is not working, or if heat sensor does not detect flame, then gas solenoid valve shuts down and water heater does not heat water.

how is heating element ? Wasit on with no water running thru it. Does it have a reset?

these units need lots of flow to start and run. Set the temp on the unit lower and the people in the shower will have to use more hot and less cold which will make the unit more stable.

Make sure breaker is turned on. If that isn't it tell me model number and maybe I can help you more

Welcome to Fixya
you have a Bosch tankless water heater your heater is not pumping out hot water?
Please send model # Thankyou

diaohragm valve or micro switch