Our Noritz tankless water heater works for a few day then when we go to take a shore it is not working. We reset and then it works for a few day. We had a techinician check it and flush it per code to relieve scale and keep sensor from tripping. But it still happens but it still happens. Any ideas

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: 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: getting error code 16. what does it mean and what

a 16 error code is typically caused by scale formation. I'd recommend performing a descale on the heater.

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.