EA error msg on Bosh tankless unit

Check pilot is clean and strong Also check sensor is clean and connections are clean and tight .

Check for obstruction in your watervalve. It has a flow meter, that needs to spin freely. Remove the watervalve and blow through it, you should hear it spin.
Also make sure you dont have an error code showing. Hold down your reset button for 5 seconds to reset an error code and get back to your set temp.

Are you looking for sell sheet pdf, or install-care manual, or service manual.
Search: GWH 715 ES manual .pdf
Adding .pdf to search parameter helps locate manuals.

Sell sheet with venting overview, technical and product specs:
http://www.globaltowne.com/manuals/sell_sheets/715-800SellSheetFINAL.pdf

Manual for ES high altitude, with installation, error codes and troubleshoot:
http://www.bosch-climate.us/files/201009031238250.GWH715ES_English_12.2008.pdf

I cannot find a service manual, or service bulletins:
http://www.bosch-climate.us/support-center/downloads/bosch-manuals/earlier-models.html

http://www.digelair.net/pdfs/TECHLIT/BOSCH/MANUALS/Bosch-ProTankless_AM.pdf
http://www.bosch-climate.us/files/201009031238250.GWH715ES_English_12.2008.pdf

Above are the manuals required to diagnose and service your error code.

EA: No flame ionization detected with water flow.
Verify that all manual gas shut off valves are open. Check gas type. Reset error code and open a water tap to cycle the heater in an effort to purge air on new installations. Cycling hot water tap on and off multiple times may be necessary. If heater still faults with EA error code, have a licensed gas technician properly purge air out of the gas line leading to the water heater. Check three wire connections to ignition group on the lower front of the heat exchanger are secure. Check gas pressure. Check venting specifications are met. Improper venting may cause premature failure of the flame sensor rod. Check that the minimum power fan speed has been adjusted to the proper value. Observe inside the viewing window of the heat exchanger when a hot water tap is opened. Sparking should be followed by a steady blue flame. If flame is unstable or yellow with proper gas pressure.

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

Error codes are starting point for troubleshooting, and solutions vary by model and unit.
E4 is Backflow temperature sensor over 309 degrees F. Appliance will close burner and lock.
Check combustion air and backflow vent piping for blockage.
Check if secondary fan connections are disconnected.
Check venting specifications are met. Long vent lengths, venting with more than three elbows, blocked vent or combination venting may cause this failure.
Check sensor resistance

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its the warm stabiliser is not work

are u using well water or hooked up to city line if well water --may be to cold for unit if water is below a certain temp unit usually goes into error or shuts down if un heated space where water heater is u may have to warm [ insulate ,heat tape etc]the incoming water usually water that around 40 degrees causes problems

BOSH AQ 250 On demand propane water heater ran out of propane, got gas now, but get EC flashing on the display and the unit won't fire? Lost manual, any suggestions. Thanks, Jim

The manual says to hold a match near the pilot while the ignitor is trying. It says that if the unit lights the pilot orifice may be dirty or clogged. Then the manual says to check the voltage on the igniter. It should be 1.3 volts DC minimum if it is not means the electronic control box is defective.

Let me know the status ...Kevin

Try this web site!
http://www.protankless.com/BoschProHome/GasProducts/BoschGWH425HN/tabid/506/Default.aspx
Copy & Paste to Google search engine.