Can i use a tankless hw heater to supply my hobart am15 dishmachine

Yes it can be converted, however you cannot buy orifice, will require a license.
https://www.rinnai.us/faq/tankless-water-heater/can-a-rinnai-tankless-water-heater-be-converted-to-a-different-gas-type

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
h

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

Clean water filter.
Delime heat exchanger.
http://waterheatertimer.org/How-to-delime-tankless-water-heater.html
Add tempering tank to preheat cold incoming water.
http://waterheatertimer.org/Tempering-tank.html
Check for bad single-handled faucet cartridges.
http://waterheatertimer.org/Crossover.html
Don't install multi-sensor computer-chip water heater to water lines and gas line and vent pipe since tankless will develop unsolvable problems.
Contact Rinnai and hear them tell you to call service technician, only to discover there are no qualified service technicians in your area who might be able to solve problem. 1-800-621-9419
Ask why the Rainnai site has much promotional information and no service manuals. Nor does Rinnai offer forum where tankless owners can freely exchange their endless unsolvable problems for all to see.

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

Grundfos RCP-96 has Flow range: 0 - 27.5 U.S. GPM
According to Amazon spec sheet:
http://www.amazon.com/Grundfos-RCP-96-UP515-55SFC-Recirculator-Timer/dp/B00128BJAO

Most tankless require .4 GPM to start burner and .25 GPM to maintain burner
Rinnai does not show C85e-1 so you will have to consult your manual to see minimum water flow requirement.
http://www.rinnai.us/tankless-water-heater/
Sample manual from Rainnai mentions 'minimum flow rate' several times but doesn't give specific number. Yet promotion blurb on page 1 says "Ultra operates at a lower minimum flow rate."
http://www.rinnai.us/documentation/downloads/U290-665x0200_Condensing_Manual_EN_FR_1-2010.pdf
Another rinnai manual mentions flow rate several times in troubleshoot section yet fails to define what that rate is:
http://www.rinnai.us/documentation/downloads/U287-1833_VB_Series_R75LSi_R94LSi_R98LSi_Manual_EN_FR_EN_FR.pdf

It might seem that tankless promoters are CTA by failing to mention specific flow rate numbers.
I think tankless promotion is a definite overachiever, and vague flow rate is one tiny example.
It proves the necessity of reading whole manual and asking questions before buying a tankless.
There's another factor to consider:
All performance numbers are based on new products in ideal circumstance, and not based on a 4 year old product located in your home.

Your flow rate may vary, especially over time, and especially if water in your area is not crystal clear, and you are not diligent with correct water softener and filter.
Many factors can affect flow rates: water pressure, number of elbows, clogs in the line, sediment, size of pipe, aireators, water-saving shower heads, local water conservation policies, water well pressure, MUD district pressure issues, your home located near end of a water main, etc.

Read tankless efficiency vrs water softener
http://waterheatertimer.org/Battelle_Final_Report.pdf
Image of tankless parts vrs tank parts
http://waterheatertimer.org/images/Compare-water-heater-parts.jpg
Bradford White tankless vrs tank side by side
Lime scale does not flush out of tankless
Tankless must have water conditions with less than 11 grains hardness
"Savings falls far short of a payback," 'without comparing service costs'
http://www.pmengineer.com/Articles/Cover_Story/8cf9e86f7c298010VgnVCM100000f932a8c0____
Sediment clogs tankless pressure sensor without softener.

blockage at pilot ,gas valve faulty ,if you have a changeover valve fault could be there

how far is the tankless from the gas meter? error code 12 means it doesn't have enough gas running to it. is the 3/4 flex true 3/4 or is it 1/2 with 3/4 threads. have you checked your BTU load on your house to make sure your 1'' pipe can handle everything else you have on the house? sounds like to me you dont have the right amount of gas to the unit.

I wonder if you have this problem below caused by a drop in water pressure from someone flushing a toilet or a washing machine. I would call the company to remedy this issue.

17. What is a cold water sandwich effect? The term “cold water sandwich effect” is a term that is used to describe the introduction of cold water into the hot water supply line during frequent on/off operation of an instantaneous water heater. The cold water sandwich effect, when present, appears as a momentary drop in hot water temperature as it is discharged from a hot water supply outlet (i.e. shower, tub, or faucet). This phenomenon is present in the operation of all instantaneous, tankless style, water heaters, but is minimized with the high tech design of Rinnai water heaters.
The technology built into the Rinnai water heaters is designed to minimize the cold water sandwich effect. Rinnai water heaters are microprocessor controlled and when water flow through them ceases, they remain in a “ready to fire state” for approximately 1 minute. If water flow through a Rinnai water heater begins within the first minute following water flow stoppage, the water heater will fire back up within 1 to 2 seconds. This minimizes the cold water sandwich effect that would otherwise be experienced with a low tech tankless water heater. It should be noted that the cold water sandwich effect cannot be removed completely from tankless style water heaters. The safety standards developed to insure the safe operation of water heaters require a delay in the ignition sequence of all gas water heaters.
While the cold water sandwich effect cannot be completely eliminated from standard plumbing systems, it can be eliminated from plumbing systems that have a supply and return hot water circulating system. Rinnai has developed 2 methods to eliminate the cold water sandwich effect in residential hot water circulating systems.
The first (and preferred) method to remove the cold water sandwich from circulating systems utilizes a small electric tank water heater (powered up) that is used with a dual purpose. The small water heater acts as a mixing tank to eliminate the cold water sandwich effect from the Rinnai water heater and it uses its electric heating element to offset the heat losses from the hot water circulating system.
The second method to remove the cold water sandwich from circulating systems utilizes a small 2 to 6 gallon storage tank installed on the hot water outlet of the Rinnai water heater. This tank acts as a mixing tank to blend the cold water sandwich with hot water and eliminating its effect at fixtures.

12 - Flame Failure or Poor Ground

1. Immediate code 12 is usually a defective gas valve, power supply problem, or defective fan motor wiring harness.

2. If code 12 occurs after a few seconds it indicates that proper operation was established, but then stopped unexpectedly.

3. Verify that fuel is being supplied to the unit.

4. Check for proper electrical ground. Unit must use a grounded power supply.

5. Check for flue blockage on inlet or exhaust.

http://www.foreverhotwater.com/service-codes.php

You should not have to flush unless the code LC comes up. but here is the flushing diagram.