Incoming air vent rheem model 21I40Dv - Rheem Water Heaters

GE is made by Rheem ... and the heater has a thermal device located inside combustion chamber that trips when heat inside combustion chamber exceeds approximately 180°F. Tripping off can be caused by ignition of flammable vapors or by malfunction of vent, incoming air supply, dirty combustion parts, or failed thermostat on gas control valve.
Following link has troubleshoot and repair steps:
http://waterheatertimer.org/How-to-repair-Rheem-TRD.html

Call Rheem and they will recommend calling installer since tankless computers are non intended as do-it-yourself.
If condensate drain is blowing out 'air' do not forget this air is deadly poison CO gas and will kill you, first giving you a headache that goes away when you are out of house. Remove affected people from home and put into fresh air and lay on side, never on back or they will suffocate. Call 911 immediately and most will recover.
Copy following link for resources and required maintenance for tankless computers that heat water: scroll down to venting and manuals and review each to check how vent lines are set up, and that condensate line is set correctly. However this information is NOT guaranteed to match each model made by Rheem as they advance their product marketing strategy to exclude as much safety information as possible for do-it-yourselfers.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
Condensate lines can clog over time. Clean line with compressed air, and soak in clorox, and swing around overhead to remove anything inside line. This line contains bacteria so do it in neighbor's yard.
Not all conditions produce vent condensate. Condensate might not form in vent line if weather is dry and the vent has good draft. But later when conditions change, condensate might begin flowing.
Condensate is caused from burning hydrocarbon fossil fuels in any gas appliance. But problem is bigger with tankless since these appliance consume so much fuel per heating event since tankless are required to heat water rapidly as water passes by in a pipe. This is why tankless require larger incoming gas line, and larger vent line made from specific materials for the vent.
Among the long list of poisonous by-products being vented outdoors into the air our planet breathes is acidic water vapor. If conditions are such that the vapor condenses before reaching outdoor, then the acidic water gathers in the vent line and rolls back toward the tankless computer, and goes down into the condensate drain and then down into your pluming drain where it can corrode pipes and add acid by-product to other environments.
If the acidic water is allowed to fall back into tankless heat exchanger instead of down condensate drain, then eventually it will chew a hole through the special nickle alloy heat exchanger (imagine the hole it will chew through household drain lines), and the surprise will not be evident for a few years until leak develops and the tankless exchanger must be replaced at great expense, plus repairs to shorted motherboard and electrical sensors.
Just don't install tankless computer water heater is best solution for myriad of problems, maintenance, and expense of owning a device that must immediately monitor incoming and outgoing water temperatures and flow rates, incoming gas flow rate and pressure, outgoing vent flow and pressure, interact with a remote control device, while monitoring burn rates and combustion temperature using a computer motherboard that is not protected from line interference or power surge, etc
Just install tank-type heater:
http://waterheatertimer.org/How-to-install-gas-water-heater.html
Gene
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If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Your gas is not being burned completely. And you are getting code 11.
These may be 2 different problems, or more, related to gas supply, incoming air, venting, electric, dip switches, product defect ... which does not leave much off the table.

Code 11 is can also be wrong gas, wrong gas pressure, incorrect grounding, wrong size gas meter, and/or gas regulator.

Gas supply:
The tankless unit has BTU rating on label.
Get a hold of gas company to look at meter sizing, and pressure, to see if the meter is correct size for whole house line demand. And gas company may red tag your water heater. For good reason, until a professional validates installation.

If home has other gas appliances, and meter is undersized for additional demand from tankless, then that can damage some appliances.

Dip switch and gas type:
Ask Rheem if your model matches the type gas you have: Natural gas, NG, and propane, LP, are different, and some tankless models work with either type gas depending on dip switch setting.

Dip switches and altitude
Ask Rheem if the dip switch setting on your model matches altitude above sea level. Different altitudes can require different dip switch settings.
If untrained person messes with dip switches then that is a risk.

Electric:
Check 120V outlet for correct polarity ... and full voltage with 80% rating on tankless nameplate ... and check grounding to unit, ... and electric line should be dedicated, and main box should have whole house surge protector to avoid power surge knocking out electronics.

Air and venting:
Inadequate venting can also cause incomplete combustion of gas ... since the unit takes bigger incoming gas line, it is logical that unit will also breathe in more air and blow out more combustion byproduct. Is the vent sized correctly? Are there obstructions in the vent, such as several bends or turns? Is there adequate incoming air supply?

Defective product:
Malfunctioning unit, bad sensors, defects, bad pc board, there are a lot of reasons unrelated to code 11 that can be causing problem.
But if you installed yourself, it can invalidate product warranty.
There was a guy who had similar problem, and sent unit back to Rheem, and they hooked it up and detected no problem and sent it back ... end of story ... guy never got it working and lost his money.

Warranty and explosions:
Rheem does not recommend installing tankless yourself because there are many potential problems, including voiding product warranty and/or blowing up house.

Gas appliances are dangerous. Inexperienced handyman should not do this installation without extensive reading about the myriad of mistakes other people made... that professionals tend to be aware of ... which is called experience.

Validate your installation:
to preserve warranty and avoid explosion:
Call Rheem to find qualified service tech located nearby who can look at installation while talking to Rheem on phone.
Your installation needs to be validated.

Since your unit requires yearly service, its good idea to find local service tech who will gladly take your money each year.
If area does not have qualified service tech, then do not install tankless, because the problems can be endless and without solution, and generally you can't fix the thing yourself. I answer questions on fixya. I see it.

Because tankless are generally not DIY, many problems are avoided by having professional installation since Rheem tells customers to contact the installer... a lot of help Rheem is ... but you are connecting a complex computer chip with sensors to 120 volt household wiring that has not been checked for polarity or correct voltage or line interference, and connecting to a gas line and burner with vent to outdoors. All these systems pose problems for tankless installations.
On top of inherent risk of gas appliance, which should only be installed and maintained by trained professionals.

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

You have Honeywell electronic gas control valve, and error code is 7 flashes.
Probably you have power vent model.
One manual from different company says: "Reset gas control using on-off button on front of control, replace flammable vapor sensor, replace gas control thermostat.
But with Rheem you also need specific steps: Remove gas burner and look for broken glass vial, and then blow out arrestor screen air intake using compressed air, clean burner parts, check for unobstructed venting, you will need new glass vial from Rheem depending on year and model number of water heater that appears on label on side of unit, or they may not have a repair kit for that model, and you might need a new gas control valve depending on model and how extensive problem was
You have Rheem water heater.http://waterheatertimer.org/How-to-repair-Rheem-FVIR.html
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
http://waterheatertimer.org/How-to-replace-thermocouple.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 link for Rheem troubleshoot resources including error codes, Rheem chat, and possible manual:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Error codes are considered start-point for troubleshooting.
Error code C4 13 is bad oxygen sensor, inadequate incoming air supply, or bad venting. Also bad PC board, or internal wiring, or temperature set too high, damaged burner parts.
http://waterheatertimer.org/pdf/Error-code-13.pdf
http://waterheatertimer.org/pdf/Bosch_Ventilating_tight_houses.pdf

Tankless require yearly maintenance to combustion chamber and burner parts.
Prescribed maintenance can correct some of the issues in error code 13.

Tankless questions are complicated because these units have many parts, and both internal and external issues can cause problems. Also problems can arise from combination of issues including maintenance, incoming water temperature, pressure, air quality, venting, water quality, water pressure, in addition to internal washers, gaskets, and parts functioning perfectly with each other over time.

Hot water only after a certain time of day indicates problem might be pressure related.
Which could be local water supply, or clog in line, or sediment on pressure sensor, failed pressure sensor, dirty in-line sediment filter, improper vent, or combination of things listed.

Rheem suggests calling service technician.
Service technicians train for years on one brand of tankless, and then see something new each day.
To understand why service technician is recommended, view number of UNanswered questions on following link showing one Rheem tankless model number.
http://www.fixya.com/tags/rtg_74pvn

I suggest avoiding tankless water heaters since all costs are energy.


Clogged pressure sensor after 2 years exposure to hard water. De-liming tankless will not prevent failure from hard water.

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Rheem makes a number of tankless models
http://www.rheem.com/products/tankless_water_heaters/

They make a tankless 95 outdoor series
http://www.rheem.com/product.aspx?id=EBA80FAA-3C0F-411D-AF83-82061C28ED1B

The 95 outdoor series spec sheet says .4 GPM minimum activation and .26 GPM flow to keep burner activated. The colder the incoming water, fewer users can take a shower at once.
http://globalimageserver.com/fetchDocument.aspx?id=ea5f0816-dfd4-4bcf-a605-79945619f5bb
The .4 GPM and .26GPM numbers are fairly typical for tankless units.
These numbers are good when the unit is new.
After a few years the number may be different because the tankless is a high-tech machine with sensors that are susceptible to particulate in the water, and susceptible to perfect-functioning of other parts in the machine.
The outdoor series spec sheet says the tankless is good to minus 30 F.
But remember that's when the unit is new.
Outdoor tankless water heaters have an electric heater that keeps water pipes inside the unit from freezing, as long as electricity is ON.
If electricity goes off, the house stays warm inside for several hours.
But a steel box located outside would get cold immediately without electric heat.
The electric heater adds standby cost to operational expense.
The tankless has a heater, but you still have to protect the incoming and outgoing pipes.
If your incoming water is very cold, the tankless heater may not be able raise the temperature fast enough to give two showers -or- even 1 shower depending on age and efficiency and capacity.
You can add a tempering tank located in naturally warm area that passively pre-heats incoming water before it enters the tankless burner.
It might be best to locate tankless inside the house >> and use direct vent through the wall for both incoming air supply and outgoing vent gas.
If incoming air is taken directly from the living space, then tankless will draw air into the house through cracks and around doors.
A lack of sufficient air, or poor air quality can cause the burner to shut down.

When buying a tankless, read the spec sheets and really ask questions about everything you don't understand.

They show code 11 as no ignition on the rheem technical page but they do not show anything for code 13. Does it say what code 13 is on the unit somewhere...maybe inside the cover? Is this a direct vent model? What size gas line do you have going to the unit? Make sure it is not undersized. How is the water flow? Does it flash the code with all the faucets on? It might be a water flow issue. Let me know more info so I can assist you further.

Is the vent fan working well and can you feel unobstructed air out the termination fitting outside?