Our rheem gas pack running on propane will turn not always ignite

There is no pilot light on your power vented hot water heater. You may as well unplug it because the induction fan will continue to run. Hopefully your propane company is responsible enough to perform a gas leak check on your propane system. After the gas is turned back on, you can plug in your water heater to start it up. Run-outs are costly so it's bet to get on automatic delivery or call when the tank is down to 30%

Call Rheem, they do not support gas change on all models:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

Gene

Water Heater Timers Save Money

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

Hi There. You have not mentioned that you also replaced the spring inside the gas valve suited for propane, please check. I strongly advise not to modify the unit's ignition system nor bypass safety device, this is for your own good. Check the gas valve spring first.

1) Rheem does not post service manuals.
Call Rheem and ask why, since the other big manufacturers, AO Smith and Bradford White do post service manuals.

2) You need new propane gas control valve, and matching combustion parts to fit existing tank.
http://waterheatertimer.org/pdf/Rheem-Water-Heater-parts-catalog.pdf
http://waterheatertimer.org/images/IMG_1826-LP-burner-450.jpg

3) Rheem does not recommend changing gas type, especially from natural gas to LPG.
LPG is higher pressure, and burns much hotter and requires cast iron burner, unlike the lighter-weight metal used for Natural gas burner.
The manifold tube and thermocouple must match the gas control valve, and gas-type and have correct thread for propane.
The combustion chamber and heat transfer surface can also be heavier metal for propane heaters.

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

Unknown if this is new installation.
New installation, you may need more gas to the unit.
Call the propane dealer.
The dip switches for selecting LP or NG may be set incorrectly.

If this installation worked before and stopped working:
Before calling service technician, copy following link for troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Error code 11 is ignition failure.
Keeping up with regular maintenance can eliminate a lot of common error codes, but the cost is greater than expected savings from owning a tankless.
Regular maintenance such as cleaning combustion parts, checking gas pressure, testing solenoid gas valve, sanding carbon off the igniter, checking igniter wiring harness, etc.

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

Before calling service technician, open following links for troubleshooting resources including Rheem phone, chat, error codes, general maintenance pdf, and generic service manual:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf
http://waterheatertimer.org/pdf/Tankless-service-manual.pdf

Error codes are considered start point for troubleshooting.
Error 11 is 'no ignition' or 'no gas'
You have checked gas and pressure, and had parts cleaned.
Other causes can include: igniter wiring, bad igniter, loose wire on gas solenoid, bad solenoid, improper grounding.

Ignition Lockout on this unit means #1 that it is set up on propane. If you are low on propane, or were low on propane and just refilled, low/no gas pressure could be the issue. If you ran out of propane, thre is now air in the gas line that needs to be fully blead out.
If propane level is not the issue, replace the ignitor.

The ignitor on these units is also the flame rectifier (flame sensor). If the unit is firing up, but the computer thinks that it is not, then it is not sensing a flame. Replacing the flame rectifier/ignitor will fix the problem in this case.

Before calling service technician, open following link for Rheem troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

C2 11 is: "inadequate gas.
Open the gas shutoff valve all the way"

Another source for error 11 shows: "no ignition"
"Ensure you have gas to the appliance.
Ensure gas type and pressure are correct.
Bleed all air from gas lines.
Ensure gas line, meter, and regulator are sized properly.
Ensure appliance is properly grounded.
Check gas solenoid valves for open or short circuits.
Ensure igniter is operational.
Check igniter wiring harness for damage."

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.

HAVE YOU TURN THE GAS VALVE TO ON WHAT MODEL DO YOU HAVE HAVE YOU RAISE THE TEMPETURE CONTROL IF YES THE GAS VALVE OR THE IGNITION CONTROL ARE BAD