I live in area code 20912 (Takoma Park Md.). Please, suggest few Plumbers in my area that have experience installing ecosense 180DVN tankless water heater. Thank you. Marcos V.

Copy following link for Rheem/Richmond/ Ecosense tankless computer troubleshoot and error code resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
C7 might mean tankless computer motherboard has gone bad
If tankless is older than 5 years, then cut losses and replace with tank-type heater so there is less maintenance and repair expense, and homeowner or local plumber can make repairs without calling tankless computer technician:
http://waterheatertimer.org/How-to-install-gas-water-heater.html
Gene

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

Feb 2013
1) Rheem/EcoSense tankless product manual does not have specifications for length. Error 11 will let you know if venting is improper.
Often, tankless are installed outside because unobstructed venting is key for combustion of the amount of gas coming out of 3/4" gas line.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

2) Copy following link for Bradford White venting: Exactly same as Rheem, but more installation detail. No maximum lengths given.
For lengths greater than 5 feet, a condensate trap must be installed. Acidic water from hydrocarbon combustion will damage metal, and destroy heat exchanger inside tankless if water drips back into unit.
http://hometips.me/Tls/Venting-Bradford-White-tankless-gas.pdf

3) Copy following link for tank-type power vent tables:
Generally, the longer distance requires larger vent diameter, and there is max number of elbows and/or air-flow restrictions.
http://hometips.me/Mar/Bradford-White-Power-Vent%20-tables.pdf

4) Otherwise call Rheem/EcoSense, and add comment saying what resources they offer.

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

1) Copy following links for Rheem tankless error codes
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Tankless-Error-code-13.pdf

2) Maintain water heater as shown in product manual to avoid common error codes.

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

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

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

Before calling service technician, open following links for troubleshooting resources and typical manuals.
http://waterheatertimer.org/pdf/Rheem-error-code-C7-76.pdf
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Tankless water heaters require yearly maintenance.
Many causes for common error codes are covered in the yearly maintenance.

1) You posted under Rheem tankless
Open following link for useful troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

2) Unit can have internal part failure for example PC board, and result is that you get no error code.
This would explain why re-setting the tankless works.

3) Unit could also have loose wire or loose connection.
Or maybe the heat exchanger needs to be de-limed.
Or incoming gas, or incoming air, or vent problem.
Or water pressure, or water flow.

4) Without an error code, the problem can be household plumbing problem.
http://waterheatertimer.org/pdf/No-Error-Code.pdf

5) Tankless repair is a large and developing field, and technicians train for years and still see new stuff each day.
Do-it-yourself tankless troubleshooting and repair might take equal amount of work.
First thing you want to do is read the manual several times.
Pay special attention to the word 'maintenance' and make sure you are properly maintaining water heater on yearly basis.
Next thing is to find qualified technician in your area, and put that person's number in your rolodex wallet. When technician comes over, ask that person for do-it-yourself tips and tricks.

6) Add a comment with your experience so other with same-similar problem can benefit.

7) 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 the exact same problem with error code 13 on my Rheem/Ecosense 180dvn . The unit ran good for at least a year, and then I started getting the same error 13 every few minutes. I called the Rheem service department, and they told me to check the vent installation as well as the gas pressure. I reinstalled the vent with new seals. I only have about 6 ft of vent, so there should be very little resistance. I checked the gas pressure, and it shows 9 in H20 pressure, which is well in the range recommended. The service center scoffed at the suggestion that it could be their circuit board. I am totally at a losss and at the verge of ripping this very expensive installation out of my attic.

1/2 inch if you are using steel pipe (which is the most hearty for outdoor installations).

Happy installation:)

That is a flame failure..there are many reason for this
be sure you have gas
there could be air in the gas line
flame sensor dirty

It has electric ignition. No pilot to light.