De-limed by following maintenance procedures with vinegar 2 hours, drained/rinsed per manual. Now unit won't heat water. Completely non-operational.

Keep filling your water reservoir with water and running it through, until it clears up, it might take a few fill ups of your water reservoir to get the vinegar taste out.

You should only use distiller water in the steamer. Never ever use tap water! This is what caused lime and scale build up.
Since it's to late, you have nothing to loose by trying this to descale the unit:

Put up to one cup of white vinegar into the reservoir. Fill 3/4 of the way with water. Turn unit on and let it heat up, but DO NOT RUN STEAM THROUGH THE LINE. Once heated up, turn unit off and let it set for hours. Drain and rinse well. Then run a water only batch through the steam cycle. There are companies that sell special de scaling solutions. But hopefully, the vinegar will work.

1) Copy following link for steps showing how to run white vinegar through Rheem tanklessx heat exchanger to partially remove scale that coats heat exchanger and reduces unit efficiency and causes error code IL:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html#de-lime

2) Tankless are prone to scale inside heat exchanger and require yearly deliming to mitigate effects. Do the required yearly maintenance to avoid common error codes.

3) Expected cost of maintenance and repair is more expensive than estimated $1-8 monthly energy-bill savings from owning tankless.

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

Before calling service technican, copy following links for general troubleshoot resources and error codes, and manusls, and Rheem contact information:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Rheem-CondensingTankless-maintenance-2012.pdf

Error IL usually means delime the unit.
http://waterheatertimer.org/pdf/Rheem-De-lime-tankless.pdf
Read your product manual for yearly/monthly maintenance schedule.
Tankless are maintenance heavy and must be delimed each year.
Deliming using white vinegar take about 1 hour, and will not restore full efficiency to unit.
Tankless have the habit of forming lime deposits inside the heat exchanger, even with softened water.
Tankless cannot be exposed to more than 11 grains hardness in water.
Don't buy a tankless next time.
Read the manual first.

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

I believe that is a water sensor error...your machine may be coated with lime preventing the machine from sensing water...generally if your unit is plumbed for water the boiler would need to be removed and de-limed...if you have a "pour over" unit...then try pouring white vineger mixed with water...50/50...into the normal fill port...let it sit for an hour or two and drain or flush...the vinegar is a safe way of dissolving the lime...phillip

Before calling service technician, open following link for Rheem tankless resources including error codes and possible manual.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Read your manual for troubleshooting, advisories and required maintenance.
Tankless are maintenance heavy.
1L means tankless heat exchanger has lime build-up.
De-lime tankless unit.
U-tube has videos for de-liming tankless, but there is more to consider:

De-liming is yearly maintenance requirement.
Tankless are prone to lime build-up
Regular de-liming will not restore full efficiency to tankless unit.
Tankless cannot be exposed to water with more than 11 grains hardness.
Temperatures over 135 can cause minerals in water to harden on metal surfaces of any water heater.

Also clean Tankless water filter each month, and clean and maintain burner and combustion chamber yearly.
The cost of maintenance and cost of expected repairs and cost of parts plus cost of original installation will never pay back the $1-8 monthly savings on gas bill. All costs are energy.
Make sure there is qualified service technician in area before buying tankless.

Upvote the help.
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.

From http://www.keurig.com/customer-service/brewer-registration-and-support/~/media/Files/Keurig%20Brewer%20Manuals/De-scaling_instructions.ashx
To begin, you will need the following:

• 48 ounces of undiluted white vinegar
• Large ceramic mug (do not use a paper cup)
• Access to an empty sink

PREPARE Step 1: Empty the water in the Water Reservoir. Step 2: Disable "Auto Off" features.
FILL AND CLEAN Step 1: Pour approximately 48 ounces of the vinegar into the Water Reservoir. Step 2: Place a large mug on the Drip Tray Plate and run a brew cycle. DO NOT USE A K-CUP, just press the BREW Button. Pour the contents of the large mug into the sink. Step 3: Repeat the brew process without a K-Cup until "ADD WATER" is indicated. Step 4: Now let the Brewer stand for at least 4 hours while still on. Step 5: Discard any residual vinegar and rinse the Water Reservoir thoroughly.
RINSE Step 1: Ensure the Water Reservoir is filled with fresh water. Step 2: Place a large mug on the Drip Tray Plate and water brew cycle. Pour the contents of the large mug into the sink. Step 3: Repeat brew process until "ADD WATER" is indicated. Step 4: You may need to perform additional water brew cycles if you notice any residual taste. NOTE: If "DE-SCALE" is still displayed after completing the procedure, repeat the de-scaling procedure above.

IL code is: water heater has lime deposits.
Tankless should be de-limed each year using white vinegar..
Search U-tube for "de-lime tankless heater" to see how to do this yourself, or call service technician.
There are special fittings that can be added to tank at the hot-n-cold ports that let you easily de-lime your water heater each year.

Typical manual shows error IL on page 33:
http://waterheatertimer.org/pdf/Rheem-RTG74IndoorOutdoor_owners.pdf

Typical manual also shows regular maintenance on page 29.
The word maintenance is used throughout the manual.

Research shows that regular de-liming will not restore full efficiency to tankless water heaters:
http://waterheatertimer.org/pdf/Battelle_Final_Report.pdf

Unplug, cool down, remove carafe and basket, turn unit horizontally over sink. It will drain faster if you remove the screw on "distributor" (nozzle). OR do not drain. Just add the plastic pitcher full of a 50% white vinegar solution, let heat then turn off for 1 hour. Drain OR add 4-5 pitchers of cold water to rinse.