Noritz tankless water heater gives error code 11

Remove the bird's nest in the flue.

The 10, 59, 90 and 99 error codes indicate that a Noritz heater has experienced a combustion abnormality. In most cases, it is the result of an obstruction in the heater's flue. Examine the flue to see if it is blocked by debris and clean if necessary.

How To Resolve The Seven Most Common Noritz Tankless ...

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Nov 16, 2015 - This error code involves a breakdown in communication between two tankless water heaters using the Quick Connect Cord. It can occur when more ...

Troubleshooting Noritz Tankless Water Heaters and Error Codes

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Error code 90 and 99 ... Action: Check for the obstructed venting, improper gas burning (flame shape and color change). Ensure the water heater gets the ...

Error Codes for a Noritz Water Heater - Waterheatertimer.org

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Code 11 is ignition failure.
Ensure that your gas is turned on.
Start by checking the vent system to ensure there is no obstruction or separation in the vent system.
Second I would recommend flushing the water heater with vinegar or Rectorseal Calci-Free. Calcium and scale build up in tankless water heaters can cause several failures that are not directly related to the specific code displayed on the heater.
If the problem persist I would look for a plumber that is familiar with tankless water heaters.

The Noritz Manual shows fixed for the following error codes:
11
21
90
99
For all other codes this is the recommendation:
Contact our sales agent if:
• Any other error code appears.

11-2-12
Copy following links for Rheem tankless error code 11, and other useful resources.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Tankless-error-code-11.pdf

Repair tankless water heater, any brand, same day, yourself for around $350 by replacing 1 part > the whole thing.
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

Replace single-handled faucet cartridge, and see if hot flows to that faucet again.
http://waterheatertimer.org/Crossover.html

Exposing tankless to hard water causes reduced efficiency within a few months, and can cause Total failure of parts within two years.
Do not expose tankless to more than 11 grains hard water.
Here is research pdf conducted by water softener industry comparing tankless andf tank-type:
http://waterheatertimer.org/pdf/Battelle_Final_Report.pdf

To solve problem long-long term, install tank-type gas water heater from local box store for $350.
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

try cleaning your spark rod inside the unit and the other rod next to the spark rod on the side of the unit. Takagi use a emery cloth, rheem brass brush, noritz a emery cloth. but make sure that both of the rods that are in the flame chamber are very clean. It miss reading because of build up on the rods.

this is usally a ignition problem...it is usally the flame sensor or ignitor giving problem..if the unit is still under warranty contact rheem...or have a qualified technician check it out..

Here are a couple things to look for:

1) flashing burner light - a flashing burner light indicates the unit is getting an error code
common error codes:
A. continuous flashing - ignition failure or abnormal combustion; look for visible water in the machine indicating a leak, check gas pressure, debris or buildup on flame rod/igniter plug, or clean unit with compressed air
B. 3 flashes - error 16, abnormal outlet water temperature; typically this code indicates you'll need to descale you unit
C. 4 or 5 flashes - exotic error codes; you should contact Noritz technical support to deal with these codes

2. If there is no flashing code, try increasing the hot water flow. In the summer time you typically use less hot water; this can result in intermittent operation of your tankless heater. Increase water flow by either: A. cleaning your showerhead and removing scale deposits B. widening your flow restrictor C. Remove your flow restrictor in the showerhead

3.If none of these resolves your problem, you probably have debris in your flow sensor. Contact Noritz technical support for a walkthrough on removing debris from a flow sensor.

The trick with these hot water heaters is to keep the filter screen clean and flush the system with CLR periodically. Code 11 is ignition error. Is your gas valve turned on?

I called Noritz error code 16 is a overheat problem. Noritz say's to flush your coil with vinegar or CLR.
Use a small pump to recirculate the CLR or vinegar through the system for 45 minutes and flush with fresh water. This worked for me.