Cant get power to my rinnai...went to turn on and it has no power to it,,checked all electical and fuses but still wont turn on

I could not find r85 model on rinnai website. There is a troubleshooting guide on rinnai website. 100000652-Troubleshooting TWH Diagnostic Codes.pdf (rinnai.us) It may help to find a solution.

Code 12 is a flame failure.
First step in diagnosing the root of the issue is to check for any separation, obstruction, or failure in the vent system.
Second step is to use the isolator kit under the heater to flush the heat exchanger with vinegar or rectorseal calci-free.
These two things are a great starting point to working on any tankless water heater. Flame failure can be as simple as the heat exchanger being clogged not allowing the sensors to work properly or the exhaust being mixed with the air intake. If the problem persists I would suggest having a Rinnai Certified Tech look at the heater.

there must have been a power interruption during fill or while there was a flow (Water will not flow when power returns)
1. Turn of all hot water fixtures. Next press the ON/OFF button on the temperature controller twice. Will reset the fault.
Hope this does it. Let me know please.
Happy New Year!

Depending on the installation location, there may be a fused disconnect near the unit. Check for voltage there. If you have power at the disconnect, open the cover on the unit and check for power at the connection point.

Has water heater been cleaned?

IF THIS UNIT HAS SPARK IGNITION THE IGNITORS ARE PROBABLY OUT OF ADJUSTMENT WHICH IS LIKE HAVING TO WIDE OF A GAP ON A SPARK PLUG . IF YOU MAKE GAP OF IGNITOR ELECTRODES APPROXIMATELY 1/8TH OF AN INCH APART IT SHOULD LIGHT AS LONG AS YOU ARE GETTING VOLTAGE FROM IGNITION COIL. CALL A SERVICE TECH

The rinnai is a computer that heats water. It is not ordinary water heater most people are familiar with, and repairs are not do-it-yourself, requiring a trained technician qualified in that brand who can diagnose both computer and water heater problems and plumbing problems.
Call rinnai for recommended local technician. Click on support tab. Note their webpage is very short on repair details, unlike companies that sell tank-type heaters... because tankless units are not do-it-yourself.
http://www.rinnai.us/tankless-water-heater
Problem might be simple blown glass fuse on circuit board or complete failure of computer and sensors.
Here is page written for Rheem tankless, that explains general complexity of tankless computers, and showing required maintenance, such as deliming each year:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
To save problems with tankless computers plus anticipated expense of maintenance and repairs, I recommend homeowner install tank-type gas water heater:
http://waterheatertimer.org/How-to-install-gas-water-heater.html
Also install one-time-use whole house surge protector, and install grounding rods to prevent further damage... lightning frequently likes the same places over and again:
http://waterheatertimer.org/How-to-wire-Whole-house-surge-protector.html
Gene
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If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Rinnai RU98e is gas water heater with .4 gallon per minute activation.
This tankless gas water heater plugs into ordinary 120Volt 60 Hz outlet and consumes 63 watts when running.

For electric tankless:
Copy following links for illustrated walk-thru and wire-breaker size calculation for electric:
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html

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

Check voltage going into the heater and at the remote terminals. Many tankless heaters also have a GFI inside their units. You can check if the GFI has power across the connections.

Flow meters can get jammed by silt or debrise. The only way that I know to check this problem it to remove & inspect the part and that takes alot of training if you have a Rinnai (not recommended for the beginner).

One thing you could check is the inlet screen. Turn off the water and power to the unit and drain down. The screen in the black plastic circle on the inlet fitting under the unit. Unscrew this and check how much grit it has collected. Clean off, replace, turn water back on, open a hot faucet to get the air out then turn the power back on. This sometimes improves the flow enough to solve the problem.