What is a code 29

no thing stated, just codes.
wow, posted to computers.

google told me its
Rheem RTGH-95DVLN-2 Natural Gas Condensing Tankless Water Heater why post this in computers, it is not.

A 29 error code indicates a neutralizer drainage failure. The neutralizer is designed to drain condensate away from the heater. If the neutralizer and/or drain becomes blocked up, the unit will flash the 29 error code to prevent the burner from being flooded.

The neutralizer has a plastic drainage tube going out of the case at the bottom left corner. You need to remove the valve on that tube to let the water drain out freely.

I had the same problem for my new Rheem.

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

No error code can mean variety of problems:
http://waterheatertimer.org/pdf/No-Error-Code.pdf
http://waterheatertimer.org/Low-hot-water-pressure.html
http://waterheatertimer.org/Crossover.html

If thermostat is set high that can also cause unit not to turn on.

Open following error-code link in downloadable pdf for your files:
http://waterheatertimer.org/pdf/Paloma-Tankless-Error-Codes.pdf

Error code 11 has to do with ignition/gas/gas pressure/electrical grounding.
This can be caused by internal part failure or combination of internal or external factors.
I suggest reading pdf, and then calling service technician who specializes in your brand.

Open typical manual to review required regular maintenance for tankless on page 29
The word maintenance is used throughout manual, indicating that tankless are a yearly budget nuisance
http://waterheatertimer.org/pdf/Rheem-RTG74IndoorOutdoor_owners.pdf

Open following link to view fixya questions on 1 model of Rheem tankless
Some older questions have information that is useful, and varied
This will give you cross section of problems that are faced by others with same/similar product as yours.
http://www.fixya.com/tags/rtg_74pvn

All costs are energy.
You can also add simple tank-type water heater that can be turned on when tankless is on the blink.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

Use following link for Rheem tankless troubleshoot: http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

I believe error code C7 is same as error code 76

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.

IL code is: water heater has lime deposits.
Tankless should be de-limed each year using white vinegar..
Search U-tube for "de-lime tankless heater" to see how to do this yourself, or call service technician.
There are special fittings that can be added to tank at the hot-n-cold ports that let you easily de-lime your water heater each year.

Typical manual shows error IL on page 33:
http://waterheatertimer.org/pdf/Rheem-RTG74IndoorOutdoor_owners.pdf

Typical manual also shows regular maintenance on page 29.
The word maintenance is used throughout the manual.

Research shows that regular de-liming will not restore full efficiency to tankless water heaters:
http://waterheatertimer.org/pdf/Battelle_Final_Report.pdf

It tells you that your water heater called for heat for more than an hr and never got hot enough to meet the demand. multiple scenarios can cause this
CAUSES

-bad sensors
-no hot water from boiler
-bad thermal transfer
-low delta T across water heater

The code # 11 is a code that warns of "no ignition" and the causes of this error code are too many to list. I would suggest that a qualified tech. perform a diagnostic test and repair.

This is not a task for the "do it yourselfer"