Question about Bosch AquaStar Indoor Natural Gas Tankless Water Heater with Vent Hood #125

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Bosch SX 250 tankless water heater will attempt to fire 3 times then EA code. I have spark through viewing window. Read troubleshooting manual. Says Check ionization electrode. There is no part in the manual with that designation. Where is it?

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The flame is sensed by a small metal rod that is immersed in the flame. When you look at the flame inspection window on the lower right of the combustion chamber, then just inside the window you should see 3 rods, and following them down below, then are connected to 3 yellow wires.The right most rod is the flame sensor. It detects the flame when the 118 volt sine wave is rectified by the flame. No flame, 118 volt P-P, flame; flame ignited, half wave only.

EA & EC codes are basically the same, the flame is not detected. EA indicated that during the initial ignition stage there were several errors, while EC tells us that the flame was undetected after the start-up had happen. This is intended to detect that the flame is not burning, and as a safety, shut off the gas supply. If you watch the right hand rod, the flame detector as the startup occurs, and on into the operational period, if you get that far, you may observe that the flame doesn't extinguish, but rather jumps above the detector rod, which also causes the safety to loose the flame retification signal, and shut down. If you vent is clear, you have tested your gas pressure according to the manuel, and the flame does ignite at all, then you likely have the wrong combustion and your CO2 will not be the value for the fuel you are using. You will need to get an expensive device called a Combustion Analyzer to be able to set the correct CO2 levels out the flue. You may be better advised to obtain the services of a pro who has this analyzer and experience using it. Most combustion analyzers need frequent maintenance to replace the O2 sensor inside to have the device read properly.

When you remove the outer cover to service and adjust the system, you should see 2 yellow dabs of sealer that cover the 2 adjustment setting screw heads. The final determination of the correct combustion must be made with the cover in place and tightened. To make that much easier, take a careful measurement from a near by wall, and floor to the center of the 2 adjustment ports with their covers opened. Reinstall the outside cover and mark these 2 points from the previous measurements, and drill a 1/2" hole at each place to allow the tool to fit into the adjustment screws while the cover is mounted. (remove the cover while you drill it!) Follow the manual for setting the P1 & P2 to the correct CO2 level. These adjustments are sensitive and take time to settle after a small tweak - go slow!

Posted on Jun 06, 2012

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This is also known as a flame rectification sensor. It basically is what the computer board uses to detect if the pilot flame is lit. When it makes an attempt to fire is there any evidence of flame ignition? This error does not mean that the sensor is bad for sure. The error could be caused because the water heater is only making three attempts to fire and then shutting down. These water heaters are very complex and have many sensors,valves, ect that are all controlled by a computer board. Some of the basic things to check for are... Make sure that you have plenty of gas pressure. These units have a built-in pressure switch and will have issues if they are starved of gas. Most of these tankless water heaters are up to 400,000 btus and a half inch gas line or undersized connector won't work well. You can also check and make sure there is no pipe dope are debris stuck in the screen inside the gas line where it enters unit. Inspect the pilot assembly for debris or obstructions and try to blow out with compressed air. Also look for any loose electrical connectors on the board or to the sensors...one may have come loose.

Posted on Sep 07, 2009

  • dejong93 Mar 08, 2011

    I have the same problem with my water heater, the tech i had inspect it says that the water heater is misfiring. With this problem it seemed more likely to adjust the gas air mixture. I have this problem only in the winter time. After resetting the air gas mixture, the problem was less persisitant, I had the tech come back and do it again, like before it was misfiring less. But not gone. As soon as warmer temps came the problem would disappear. My unit sits in the cold crawl space of my house, and has fresh air intake from the basement, it exhaust through to the outside world. I have a 1" delivery line with more than adequate gas pressure. Its a real pain in the ***, when it comes on code and i have to reset it.

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My bosch tankless water heater is flashing ae


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

Sep 26, 2011 | Bosch & Tankless LP Hot Water Heater

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It often flashes ea or af and doesnt want to light


Before calling service technician, open following links for troubleshoot resources including common error codes, Bosch contact information, link to service manuals, and possible product manual
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/2400ESTechSupport/Troubleshooting/tabid/1295/Default.aspx

Call Bosch 800-642-3111
Multiple error codes can mean PC board failure.
AF might be A9, but not sure.
EA is 'no flame ionization detected with water flow'
  1. Verify that all manual gas shut off valves are open.
  2. Check gas type.
  3. 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.
  4. Check three wire connections to ignition group on the lower front of the heat exchanger are secure.
  5. Check gas pressure.
  6. Check venting specifications are met. Improper venting may cause premature failure of the flame sensor rod.
  7. Check that the minimum power fan speed has been adjusted to the proper value.
  8. 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.

Aug 11, 2011 | Bosch AquaStar 2400ES-NG

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Bosch GWH 715 ES flashing EA code. This unit was working fine for over a year so I am assuming gas pressure can't be the problem? The spark is flashing and the unit lights for about 2 seconds then...


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.

Jul 07, 2011 | Bosch & Tankless LP Hot Water Heater

1 Answer

Bosch 250 sx ng tankless water heater showing error code. checked fuses and they are fine. tried resetting many times still not working


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


Best place to start is troubleshoot section in manual. Page 24
http://www.boschhotwater.com/Portals/7/TechManuals/250SX_English.pdf

Problems range from air supply, gas supply, venting, part failure or combination of listed things.
Don't forget, tankless require yearly maintenance, outlined in manual, and cannot be exposed to more than 11 grains hardness in water, and should be de-limed each year.


All costs are energy.
I suggest reading entire manual several times, so you are pro about your tankless water heater.
Even with this knowledge, trained service technician will have to be consulted
some day, and tankless should never be installed if factory trained technician not available in area.

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

Install tank type water heater that can be put online when Bosch is not working
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.

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Bosch instantaneous gas hot water not working. sounds to be sparking but not lighting and heating water. The gas is turned on. Just moved into this house so new to the machine with no manual. Comes up with...


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

Read manual cover to cover, make sure tankless receives yearly maintenance as outline in manual.

Add a comment with your experience so others with same-similar problem can benefit.

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.

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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.

Add a comment with your experience so others with same-similar problem can benefit.

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.

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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

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