Code 11 is ignition failure. The fix is almost always this, shut off power and gas. Remove front cover. find a small 3" rectulanguar cover with 3 wires going to it and remove this. there are three probes a flame sensor rod and ignitor. carefully clean the deposits off with emery paper and reinstall.

11 code = Ignition Failure
12 code = Flame Loss
90 code = Improper, or Poor Combustion

For more assistance I would need to know your model# and how long it's been installed.

Probably a 12 or 21 code. Neither of which a Consumer can do ANYTHING about. Call Noritz 1-888-382-6568 and they will have a Regional Service/Repair Field Engineer call you and diagnose problem.
This is a sophisticated appliance unserviceable to Consumer but you may diagnose it with the help of the FE for Service Contractor to repair.
N069M-DV was discontinued 3 years ago replaced by N0751M-DV. Have you checked the inlet filter since you bought it? Is it on good soft water? It's a strong pretty dependable unit IF INSTALLED PROPERLY and MAINTAINED.

Try this. take the cover off and see if the problem still exists. Once I found out that the problem did not arise with the cover off I fashioned 4 brackets to hold the cover off 1/2". Since then I have not had a single problem and the unit works great.