Unit flashes the number 20

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.

Hello
If you have a gas water heater and its a few years old and it has an electric fan for exhaust unplug the fan motor from out let and plug it in again this will rest your hot water computer and sensors. If the burner comes on which you will hear right away,, then it means your flame sensor needs cleaning its a 3 inch rod its infront of the door opening or water control below,,, slide cover off and one screw is holding the flame sensor rod. also look for a flashing red light down by the cntrols if it is flashing call a service man, in you need a computer board or module replaced if its a rental?,, its free. Please if this is Gas if you are not sure Call service man right away if its electric water heater Call for service likwise dont attempt repairs unless you need to rest your fuse on the electrical panel. Careful please lives could be in danger if you attempt anything you are not sure of Dont touch it!


Joe

Are you asking about tankless gas or tankless electric?

You posted under Tankless gas water heater: gas type tankless plugs into standard 120Volt household outlet to power circuit board. You need larger gas line than used for tank-type gas water heater.

If you are asking about volt and amp draw of Tankless electric, then that depends on specific model number.
For example, if each tankless element draws 3500Watts, and unit has 3 elements, you will need 3 additional 20 amp 240Volt circuit breakers. Volts x amps = watts. 3500 watts divided by 240Volts = 14.58 amps. At full blast, this unit would draw 43.75 amps and will cost more to operate yearly than tank-type electric water heater. If unit has 4500 watts elements, then it will draw 56 amps at full blast, and use a good percentage of household power.

Tankless water heaters have no hot water in power outage. This is true for gas and electric models.

Additional resources:
http://waterheatertimer.org/images/Compare-water-heater-parts-650.jpg
http://waterheatertimer.org/pro-n-con.html
http://waterheatertimer.org/pdf/Bradford-White-on-demand-tankless-service-manual.pdf

2 green flashes is 'High Water Temp.'
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html

Typical energy smart manual:
http://waterheatertimer.org/pdf/Whirlpool-energy-smart-electric-manual.pdf

3 flashes is Temperature Sensor failure.
4 flashes is Upper element
5 flashes is Lower element

Troubleshoot section says:
1) Make sure access doors and insulation are installed.
2) Check elements for resistance of 5-25 ohms (if element has a short in center of element, it might not trip breaker)
http://waterheatertimer.org/How-to-test-water-heater-element.html
3) replace element and reset control system.
Buy ordinary 4500 Watt element from hardware store.
http://waterheatertimer.org/How-to-replace-water-heater-element.html

4) I also suspect the self-diagnostic control box.
Manual says: Repair parts may be ordered through your plumber,
local distributor, home improvement center, or by calling
1-877-817-6750.
You need serial number, product number and model number from label on side of tank.

check the wiring connections for your remote. The FF is related to communication problems with the remote. You should also reset the unit by disconnecting electricity, waiting 20 seconds, and then reconnecting electricity to the heater.

Here are a couple things to look for:

1) flashing burner light - a flashing burner light indicates the unit is getting an error code
common error codes:
A. continuous flashing - ignition failure or abnormal combustion; look for visible water in the machine indicating a leak, check gas pressure, debris or buildup on flame rod/igniter plug, or clean unit with compressed air
B. 3 flashes - error 16, abnormal outlet water temperature; typically this code indicates you'll need to descale you unit
C. 4 or 5 flashes - exotic error codes; you should contact Noritz technical support to deal with these codes

2. If there is no flashing code, try increasing the hot water flow. In the summer time you typically use less hot water; this can result in intermittent operation of your tankless heater. Increase water flow by either: A. cleaning your showerhead and removing scale deposits B. widening your flow restrictor C. Remove your flow restrictor in the showerhead

3.If none of these resolves your problem, you probably have debris in your flow sensor. Contact Noritz technical support for a walkthrough on removing debris from a flow sensor.

I had the exact same problem. I even replaced the first unit with a second unit...because I was sure I hooked everything up correctly. Then I called their support line and and felt very stupid. They asked one question "are you plugging in the Quick&Hot into the same electrical outlet as the garbage disposal"?. I said yes..and the garbage disposal works fine (thinking that this indicates a good electrical outlet). She then said "That outlet works off of a switch so no electricity is getting to the Quick&Hot until the disposal is turned on). Gosh darn it...that made total sense. I then tested this out by plugging an extension cord into a different outlet and it worked fine. Boy...do I feel stupid. Hope this helps.

in order to reset the unit you will have to turn the temp all the way down then unplug the unit for 5 min,, remember it is a computer and it knows, after plugging in back in after the five min, reset the temp open up a fauset while doing this, that way it will be regestering the flow of water to set the temp by

I had the same problem with my tankless waterheater (flashing c4 76 alternately). I called Rheem
tech support and they had me 1 power down the remotepanel 2 unplug the unit from the wall 3 remove the cover 4 remove the wires for the remote panel from the circuit board and pull the twisted pair that goes to the remote out from the bottom of the unit. 5 reinstall the cover 6 plug the unit back
into the wall and turn on the hot water see if it works. It did in my case and they are sending me a new remote panel. I hope it helps.........