Ao smith tankless 310 has a code 10

page 16 in instructions that came with unit.

Copy and paste https://www.aosmithatlowes.com/media/1378/tankless-electric-2-4-chamber-installation-manual-and-use-and-care-guide-100285618.pdf

Here you are Dorothy

AO Smith code 991 Solution for error code 991
Check the gas type of the water heater. Inspect the environment around the water heater. ... Check if there is grease and/or dirt in the burner (Part #101) and the fan motor (Part #103), especially if the water heater has been installed in a contaminated area.

Error code '991' for type ATI-110C-N by AO Smith. Cause and ...

More help here, but you probably need a service call, especially if it is a gas water heater.

https://www.google.com/search?q=error+code+of+991

..

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

call a plumber or get a key from a plumber supply shop

OMG 95 PSI is too high a pressure for a tankless! What was the W.C. in inches on the manometer?
Also on a T-K3 12 isn't a Code but a partial Code. You need an R/C to make this easier as counting led flashes produces wrong codes.
you'll have to find the correct code it's throwing not a partial.
And put a Pressure Reducer on this to below 60 PSI. 95 PSI is only impressive when it blows the tubing out after a few years.
Call Takagi in California not A.O. Smith in TN and they'll help someone fix this

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

If tankless computer is less than 5 years old, then call Rheem for local technician qualified to work on this type of computer that heats water.

If tankless is older than 5 years, then replace with tank-type electric water heater for $285 from Lowes.

Avoid Rheem, Richmond, Palmoa, GE water heating products since this company does not post service manuals.

Choose AO Smith, American, State, craftmaster, Whirlpool etc.

Gene
h

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

Tankless require yearly service to keep burner and combustion parts clean and check electrical connections, gas solenoid, gas pressure, venting, etc.
Read product manual for advisories and recommended maintenance.
Yes, aren't you glad you saved the manual.
Always check that local area has affordable and qualified service technician for your brand before buying tankless.
Before calling service technician, copy following link for general troubleshoot resources, including some manuals, and links to Bosch.
http://waterheatertimer.org/pdf/No-Error-Code.pdf
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Try turning temperature down.
The fact there is no error code, and the gas is not firing correctly, means you have a small unit with no error codes and PC board has failed ... or it means you have a unit with error codes and possibly bad PC board.
If problem is the PC board, then Bosch will send you new board, and expect same level of repair success as though your computer's motherboard was replaced.

You can buy ordinary box-store tank-type heater and install yourself same day for about $325.
Then maintain and fix it yourself. I recommend AO Smith/American/State/Reliance/Kenmore/Whirlpool since these are easy to maintain with clear directions in manual, plus AO Smith posts service manuals for the whole line of products, and any local plumber can fix them with ez-to-locate generic parts.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

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

the sch 40 venting is no longer code , it has to be upgraded to a more heat resistant pipe called 636 pipe , it is also a plastic pipe but can withstand alot more heat. the 636 pipe goes together with a acid glue/primer, you have to place primer on pipe then the glus and push peices together hold for a few secs and your good. hope this helps you