My noritz N-0751-M tankless stopped producing hot water. No error messages, display reads 140 degrees Tried unplugging resetting multiple times. Sounds like it's starting up, no hot water.

SOURCE: No water flow from hot water tap with a rinnai tankless water hea

Its A Possibility The Left Over Water In The Hot Is Frozen. If Your Line Is Exposed Outside Somewhere It Can Easily Freeze Up. Turn On The Hot Water Everywhere In The House And If Accessible Check The Lines To See Where The Warmth Ends. You Can Leave One Off Over Night In Hopes That It Will Eventually Defrost.

SOURCE: BOSCH AQUASTAR 2400ES NATURAL GAS TANKLESS HOT WATER HEATER

Q. FA - Gas leakage error, gas valve circuit not closing properly
A.

1. Disconnect power supply cord and check wire connections on gas valve and the two connectors on the control board.
   
2. Flow water out of a hot water tap above the minimum activation point of .8GPM. Measure voltage at the gas valve wire connector. The connector should measure 24VDC between the left pair of wires and 24VDC between the right pair of wires when the unit is operating. If voltage is not correct, contact Bosch Water Heating for further instruction.
   
3. Gas valve may be defective, contact Bosch Water Heating for further instruction.

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: 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?