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

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Need manual for AQ 250 SX NG

Need venting requirement

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johnny rebel

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SOURCE: Bosch Tankless water heater. model AQ 250 SX

Error codes F1 and F2 do not show among common error codes.
Call Bosch 1-800-642-3111

Before calling service technician, open following links for Bosch troubleshoot resources:
Error codes are considered start-point for troubleshoot.
Multiple error codes can indicate PC board failure.

Posted on Aug 11, 2011


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Related Questions:


No hot water

Before calling service technician, open following link for Bosch troubleshooting resources including Bosch contact number and possible manual:

Tankless water heaters require yearly maintenance to check gas pressure, inspect and clean burner and combustion parts, inspect vent and vent drain, clean air filter, check water flow, de-lime the heat exchanger etc.
This maintenance can stop ordinary problems from occurring, and can be done by the homeowner by reading Bosch service manuals for specific model number.
The continual maintenance, and cost of repairs and parts, and cost of professional service are more expensive than expected $1-8 monthly energy savings from owning tankless.

Fix most tankless problems yourself, same day, for about $350.

I have a bosch aqvastar 250 sx ng error code EC keeps appearing

Q. EC - Ionization failure during operation
  1. Verify gas type (See Fig. 2 in installation manual) corresponds with the type of gas supplied to the heater.
  2. Verify the three yellow wire connections to the set of electrodes (underside of the burner assembly) are secure.
  3. Verify that venting meets specifications per chapter 3.6 of the installation manual. Improper venting may cause premature failure of the flame sensor rod.
  4. Check gas pressure. See Bulletin TWH-G2-03.
  5. Check and adjust CO2 readings. See Bulletin TWH-G2-12.
  6. Gas valve or flame sensor may be damaged. Call Bosch Water Heating with observations and results of previous steps.

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:

Best place to start is troubleshoot section in manual. Page 24

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:

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

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.

Tested my bosch 250 sx with no gas hookup a2 error showed up.I s this possible wit no gas hookup yet?

1) Error code A2 shows on following link:

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.

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.

I have 250 sx and a PLUMBER came and told me we have water in the gas valve, and wants 620.00 just for the part is that a common price? model aq 250 sxng serial 7703311002 can ipurchase the part &...

Depending on what part is being replaced, it may sound high but the gas valve is about $300 and the water valve about $200 street price. its also a time consuming job.

Our Bosch 2400E NG tankless water heater is displaying the EC code. I've checked the ionization electrode (rubbed it with a pencil eraser as instructed once before when we had this problem) and I also made...

Had same problem on my five year old water heater (ec error). Didn't figure it was a gas supply problem after five years but double checked to see if the gas bill was paid. It was.

Cleaned the contacts on the two sensors that are clamped to copper pipes inside. Still had error after powering up. Held the error button in for about five seconds, and the blinking EC code went away.

Bosch on demand tankless water heater gwh 2400 E LP error code "

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

Ec code come up & no hot water bosch aquastar sx 250

Open up the front cover - look at the printed curciut board and see if you have two or three capacitors that the tops are slightly raised...if so, those capacitors on the board need to be replaced...they should be competly flat.


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