Rheem 81v40 Just stopped working

Most likely bad PC board.
The fuse stops damage such as fire, but the PC board probably needs to be replaced.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Other causes might be wrong polarity on 120 volt outlet, use a circuit tester to make sure the hot, neutral and ground are correctly connected.

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

P1 clean water filter:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html#filter

Gene

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

1) Rheem 81V40 electric water heater ... manufactured pre 2009 ... posted serial number does not match manufacturer
http://waterheatertimer.org/pdf/Find-Age-of-water-heater.pdf
http://waterheatertimer.org/pdf/Rheem-Ruud-2009-water-heater-parts-by-model-number.pdf page 5

2) Possible date of manufacture 11-1994

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

Rheem does not post service manuals, but other manufacturers do.
Copy following link for troubleshoot by type of gas control valve.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Also, scroll up on same page, on right side for heading title 'Pressure switch' for troubleshooting the pressure switch.

Don't forget to check anode rod to protect steel tank from rusting.
http://waterheatertimer.org/Replace-anode-rod.html
http://waterheatertimer.org/How-to-maintain-water-heater.html

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

PC board is probably bad.
Rheem, Richmond, Ruud, Paloma, etc will send you another PC board, and hopefully the success rate will equal success rate of replacing motherboard on your computer.
Before calling service technician, copy following link for troubleshoot resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-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.

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

yes it is.

if you dont get any code then it is the circuit board..you will need to contact rheem or have a qualified technician check it

you can call Rheem

Get a new one cause the water will rot and mold inside the base plate.  Have your homeowners insurance cover the cost.