Error code 78 on Noritz tankless - Noritz Water Heaters

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 water heater gives error code 11

This worked for me in the same situation. There is a filter inserted into main gas/ water control valve that senses water flow restriction. The sensor is connected to the gas valve. If it senses inadequate water flow it tells the gas valve to shut down so the water in the heater won't boil. Very expensive part. If you do find the filter clogged, a sediment water filter shoud be install on the inlet side of the water piping.

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.