Water Heater Won't Fire up

For a Noritz tankless water heater, error number 78 indicates a problem with the fan motor. The instructions below will help you clear the problem number 78 on a Noritz tankless water heater:

1. Turn off the power to the tankless water heater by either disconnecting it or switching off the circuit breaker.
2. Verify that the fan motor is clear of any obstructions or debris that may be preventing it from operating properly.
3. Check the fan motor is receiving power by measuring the voltage across the fan leads with a voltmeter. Verify that the electrical connections to the fan motor are secure if there is no voltage.
4. If the fan motor is broken or not operating properly, it may need to be replaced. For further assistance with the repair or replacement of the fan motor, you can contact Noritz technical support or a certified HVAC specialist.
5. After resolving the issue with the fan motor, switch off the power to the tankless water heater for at least 30 seconds before turning it back on. This will clear the error code and restore normal operation to the device.
6. If you are unclear or uncomfortable with any of these processes, you should seek the aid of a certified HVAC specialist or Noritz technical support.

Error Code 20 on a Noritz tankless water heater (model EZ98DV) is typically associated with an issue with the "priority" function, which is a feature that allows the water heater to prioritize certain uses of hot water over others.
When the "priority" light is flashing and error code 20 is displayed, it typically means that there is a problem with the priority function and it needs to be reset.
To fix this issue, you can try the following steps:

1. Turn off the power to the water heater by turning off the circuit breaker or removing the fuse.
2. Wait for about 10 seconds and then turn the power back on.
3. Press and hold the "priority" button for about 5 seconds, until the "priority" light turns off.
4. Turn the water heater back on and check to see if the error code has cleared and the "priority" light is no longer flashing.

If the error code 20 still appears and the priority light is flashing, it's best to consult the manual or a professional technician to diagnose the problem.
It's important to note that the error code 20 can also be caused by other issues such as, faulty thermistor, faulty thermistor harness, faulty PCB, etc. So, it's best to get it checked by a professional.

Replace single-handled faucet cartridge, and see if hot flows to that faucet again.
http://waterheatertimer.org/Crossover.html

Exposing tankless to hard water causes reduced efficiency within a few months, and can cause Total failure of parts within two years.
Do not expose tankless to more than 11 grains hard water.
Here is research pdf conducted by water softener industry comparing tankless andf tank-type:
http://waterheatertimer.org/pdf/Battelle_Final_Report.pdf

To solve problem long-long term, install tank-type gas water heater from local box store for $350.
http://waterheatertimer.org/How-to-install-gas-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

There are many reasons a tankless heater will stop heating water. The first thing I would look for is a flashing red light on the burner indicator. The flash break down goes as follows

continuous blinking - typically means ignition failure or the unit is overheating; look for visible water inside the unit, have your gas pressure checked, or check the flame rod/igniter for buildup of debris

three blinks - typically indicates 16 error code; typically resolved by performing a descale

4 or 5 blinks - exotic error codes; for these you should definitely contact Noritz tech support

If there is no flashing light, first check your filter for debris. If the filter is clean, your flow sensor is probably stuck. Again I'd recommend contacting Noritz tech support to help you clean the flow sensor.

That unit has two flow sensors. It needs to register flow through both sensors in order for it to fire. If one of the flow sensors is stuck or if there is scale blocking flow through the heat exchanger, it will not fire. I'd recommend contacting a servicer to clean the unit.

Check thermocouple , sounds like it's not sensing flame.

F76 is a communication error between two quick connected heaters. To clear the code, disconnect power from both heaters, wait 20 seconds, then reconnect power.

Three flashes typically indicates the unit is overheating due to scale. I'd try a descale initially and see if that remedies the problem.

does the fan come on? this has to happen before it will even try to start if it doesn't your problem goes farther into the unit,, normal pracess if the fan then the ignitor then the flame, It could be in the circuit board most people that have gone with the tankless don't clearly ask the question but that is normal, but if you could clearify the procedure of what it is doing to this point i could be more helpful to you---- e-mail me what is happeing diffrent then what it use to do [email protected]

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.