A.O. Smith Water Heater. What does error code of 991 indicate?

Error codes for both types of honeywell gas control valves appear on following link...
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#honeywell

Whirlpool no longer sells water heaters ... but in the past, they sold the AO Smith brand flue damper and atmospheric heaters ... both use different Honeywell gas controls.

Whirlpool sold the AO Smith brand flue damper, and the atmospheric models ... both models have different honeywell gas controls...
Error codes, service manuals and troubleshoot appear following link:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#honeywell

There is no specific service manual available for the flue damper series in 2019

Maybe this error code chart for AO Smith Power vent will help you figure it out. Also link to AO Smith website. Good luck. J

https://www.hotwater.com/support/gpvh-50

Hello, Frazell -

If your A. O. Smith water heater is new, it probably came with an owner's manual. Find where you put yours and check the manual to find out what the ECC code means.

From an owner's manual for a particular A. O. Smith Hybrid Heat Pump Water Heater, the code ECC means the heat pump compressor is not functioning.
Source:
https://www.manualslib.com/manual/755258/A-O-Smith-Hybrid-Electricheat-Pump-Water-Heater.html?page=17#manual

Best wishes.

Copy following link
http://waterheatertimer.org/pdf/AO-Smith-heat-pump-service-manual-321547.pdf

Contact AO Smith for qualified technician in area.
Don't buy expensive water heaters.

Gene
h

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

Why is it always Rheem problems?
Every water heater problem at fixya is Rheem.
And Rheem doesn't post any service manuals, like the other two big manufacturers, AO Smith-American, and Bradford White.

Rheem 2012 manual says if error 13 still displays, then contact installer or service technician. Mo Money buddy.
This is about oxygen sensor, poor combustion, bad venting, inadequate air supply, failed sensors, etc.
Get more fresh air to unit and see if that solves problem. The call service technician, and get out wallet.
Copy following link for Rheem-richmond tankless troubleshoot.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Maintain water heater according to instructions in manual to avoid common error codes. Of course this means you have to service the unit each month, and each year, without guarantee the thing will work correctly.


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

Re- set code!!!!
We have a Takagi TH3 DV 540 model.Air intake got blocked with snow, condensation etc.Once we cleared that then you just have to re-set it to clear the 991. On our model there are 4 tiny buttons across the bottom (Take off front cover) to find them. of the computer board assembly bottom left corner. Push the two buttons on the right simultaneously hold for 15-20 seconds or so, then turn the Takagi off then on again- should work now!
If you have a different model then those buttons will be in the bottom left corner still but running vertically- try doing as above with the bottom two buttons. We had to go without heat and hot water for 2 days until we could get hold of someone to tell us this. We called Seneca Supply 716-852-4744. Good luck

You have AO Smith tank-type power vent water heater with FVIR flame arrestor.
1) I believe this system has White Rodgers intellivent gas valve, with led indicator lights.
To test if valve is operational:
-NORMAL operating mode displays no lights on gas valve.
-Unplug unit from electrical outlet and plug back in. All lights on gas control should display for 1-5 seconds.
-Press BOTH Hotter and Colder temperature buttons for one second to 'wake up' the control, and release buttons and LED will display temperature.
-Press Hotter or Colder and see if any indicator light shows on gas valve.
This will give baseline if gas valve is functioning.
-Intellivent gas valve requires outlet that is wired 100% correctly. Test outlet with circuit analyzer.
-Water heater must be properly grounded for intellivent to operate.

2) Open following link to identify gas valve and download possible service manual with error codes and testing procedure. Service manual is a large file and will probably not load on dial-up.
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html#intelli

3) Open following link for AO Smith manuals and service handbooks.
Shows same intellivent service manual, and shows manuals for power vent, but does not specifically list the GPS75 series
http://www.hotwater.com/resources/product-literature/service-handbooks/

4) Take a moment and rate answer:
And 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.

AO Smith uses the Honeywell ICON gas valve with green indicator light.
Some models use White Rodgers Intellivent with a row of indicator lights.

The gas control blinks the error code:
Open following links to identify gas control thermostat and read possible error codes:
http://waterheatertimer.org/pdf/Honeywell-Gas-Valve-LED-Codes-2000.pdf
http://waterheatertimer.org/BW.html#Temp
http://waterheatertimer.org/How-to-adjust-water-heater-temperature.html#intelli

to clear the 991 Takagi code, simultaneously press the bottom 2 grey buttons of the four just to the left of the flashing LED light. When the LED stops flashing, release and then press the reset button on the black panel about 8 inches above that