WHAT DOES THE ERROR MESSAGE F76 MEAN?

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.

F76 is usually a communication error between the remote and the heater. you may have just unplugged something inside the unit while it had power (don't do that). Just unplug the unit from the wall (or flip the breaker) and wait 10 sec and plug it back in again and the problem should fix itself. Otherwise there my be a loose wire going to your remote. In which case, try unplugging the remote and unit for 10 sec and plug the unit (only) back in with the remote disconnected. run your hot water and see if it works. if so it could be a problem with the remote or its wiring.

Go to the manual or go on line for the manual and look up the code and its meaning.

Copy following link for general troubleshoot and error codes:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Error code 36 does not show in any resource, including 2008 service manual, or 2012 product manual.
Check that remote control display is illustrating the correct number.
For example there is error code 35.

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Tankless require yearly service to keep burner and combustion parts clean and check electrical connections, gas solenoid, gas pressure, venting, etc.
Read product manual for advisories and recommended maintenance.
Yes, aren't you glad you saved the manual.
Always check that local area has affordable and qualified service technician for your brand before buying tankless.
Before calling service technician, copy following link for general troubleshoot resources, including some manuals, and links to Bosch.
http://waterheatertimer.org/pdf/No-Error-Code.pdf
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html

Try turning temperature down.
The fact there is no error code, and the gas is not firing correctly, means you have a small unit with no error codes and PC board has failed ... or it means you have a unit with error codes and possibly bad PC board.
If problem is the PC board, then Bosch will send you new board, and expect same level of repair success as though your computer's motherboard was replaced.

You can buy ordinary box-store tank-type heater and install yourself same day for about $325.
Then maintain and fix it yourself. I recommend AO Smith/American/State/Reliance/Kenmore/Whirlpool since these are easy to maintain with clear directions in manual, plus AO Smith posts service manuals for the whole line of products, and any local plumber can fix them with ez-to-locate generic parts.
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

Error code means that you have electronic gas control valve.

Copy following link to identify gas control valve, read error code meanings for each, and download service manual relevant to each gas control, but not specifically Rheem since rheem does not post service manuals.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

The fact that water heater restarts, means that water heater is getting gas, getting sufficient air for combustion, thermister is ok, gas pressure is good, etc.
The fact that you unplug and replug water heater and it works, shows that you have power vent model.
Since water heater worked correctly before, 2 flashes with Rheem power vent model could mean that pressure switch has failed.

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Water heater is not 100% identified.
Unknown if this is gas or electric heater.

Problem posted under Whirlpool water heaters typically made by American water heater company.
Call Whirlpool 877-817-6750.
They will ask for model number and serial number located on label on side of tank.
Call is answered in USA by trained person who can answer specifics about that model, including warranty, age, regular maintenance, error codes, and possible solution for that specific model and serial number.
I have found these folks to be helpful.

Whirlpool manuals do not show that specific model:
http://www.whirlpoolwaterheaters.com/support/manuals.aspx

If you have the energy smart electric water heater with electronic control board, then error code explanation shows on the control board. Error 1 or a single flash, is start-up failure and requires tank to be full of water. Read page 10 of manual. Make sure water heater is full of water and water is coming full stream out of tub spout before turning on power. Also disconnect power from unit, make sure water heater is full, and then reconnect power to see if unit resets.
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html
http://www.whirlpoolwaterheaters.com/downloads/6510306.pdf

Questions might be asking for a manual, and asks what error A7 means, and asks how to fix error problem, but model number of Bosch heater is not given.
Error codes are start-point for troubleshooting, and can include multiple causes.
So following answer provides general do-it-yourself resources, without saying that problem can be 100% diagnosed or fixed by homeowner.

1) Error code A7 is outlet temperature sensor fault.
Problems include: need for descaling, dirty inlet water filter, debris in faucet aerators, dirty wiring terminals, bad wiring harness, or bad temperature sensor.
http://waterheatertimer.org/pdf/Bosch-GWH2400ES-error-codes.pdf

2) Before calling service technician who can test failed parts and catch tankless up on yearly maintenance, open following links for Bosch resources including error codes, phone number, possible manual, and descaling instructions, and cleaning inlet filter:
http://waterheatertimer.org/Troubleshoot-Bosch-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Rheem-De-lime-tankless.pdf
http://www.boschhotwater.com/Portals/7/TechBulletins/TWH-G1-12_Cleaning_inlet_filter.pdf

3) Product manual: Question posted under model 125HX-LP
Open following link for possible manual:
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/125HXTechSupport/InstallationManuals/tabid/542/Default.aspx

4) Do it yourself service bullitens for 125HX-LP
http://www.boschhotwater.com/HelpfulResources/TechnicalSupport/BoschAquaStarModels/125HXTechSupport/ServiceBulletins/tabid/548/Default.aspx

5) Take a moment and rate answer:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

F76 is a communication error. It usually occurs if you connect or disconnect a quick connect cable or remote control when the tankless heater is connected to electricity. (If you have a quick connect system, make sure you only have 1 remote and 1 quick connect cable.) To get rid of the code, try disconnecting electricity for 20 seconds, reconnecting electricity, and turning the remote on. If the code returns, you may need to replace your quick connect cable, remote cable, or even remote control

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.