My noritz tankless does't start after we cut the electricity for a couple hours

SOURCE: Noritz tankless water heater not producing hot water

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.

SOURCE: Noritz tankless water heater/dishwasher not hot enough to clean

You are doing everything you can. Your dishwasher probably isn't drawing enough hot water to activate the unit so opening the faucet and flowing more water will activate the unit. Just try to adjust the flow from the faucet to a point it, plus the draw from the dishwasher, will activate the unit. This will come with trial and error as I am sure you have already experienced. Also, open the dishwasher when it does get filled and check the water temperature. You might have the unit set at a low discharge temperature. Do you have a touchpad to control the water temperature adjustment?

SOURCE: what is error code 59 on a noritz tankless water

The 59 code is typically caused by insufficient gas supply to the unit. It can also be caused by obstructed exhaust flow, stuck exhaust damper (located directly on top of the unit's exhaust), insufficient makeup air, or improperly installed venting (i.e. too long or too many elbows).

I would recommend initially checking the incoming gas pressure at the gas connection on the unit. The gas pressure should not drop below 5" water column for a natural gas unit, 8" for a propane system (the unit need to be operating at its maximum output).

SOURCE: Noritz Tankless error code 16

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?

SOURCE: error code 14 shows on the remote for a noritz

This means the thermal fuse has broken and needs replacement. The thermal fuse is a white cord which wraps around the heat exchanger. It typically breaks if the unit is excessively dirty and sooted. Before the fuse is replaced you should make sure the unit is cleaned with compressed air and descaled.