What is the difference between Rheem part number sp14218a and sp14218 b .?

The burner cover plate for your Rheem RRNL-B030JK08E unit can be obtained from an authorized Rheem dealer or distributor. You can visit the Rheem website to locate a dealer or distributor in your area. Alternatively, you can contact Rheem customer service for assistance in obtaining the burner cover plate. Be sure to have the model and serial number of your unit available when contacting Rheem customer service.

Contact rheem about model differences.
Shop around for cost comparison.
Copy following link:
http://waterheatertimer.org/How-to-install-gas-water-heater.html
http://waterheatertimer.org/Which-is-best-gas-water-heater.html
I usually recommend avoiding Rheem, but others disagree.
Gene
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If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Question posted under Rheem tankless water heater:

Call Rheem at 800 432 8373
They will need serial number located on label on side of unit.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Usually I recommend that people tear out their tankless water heater and sell it on ebay, and then install tank-type heater from different manufacturer:
http://waterheatertimer.org/How-to-install-gas-water-heater.html

I would be very reluctant to connect used gas appliance without a product manual, and service manual.
http://waterheatertimer.org/images/Exploded-house3.jpg

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 or bulletins.
It's how they treat customers. I do not recommend Rheem because of this problem.
They must expect their customers to pay for service call from Rheem-loyal technicians.

Here are resources that might help.
Rheem: 800-432-8373

http://waterheatertimer.org/pdf/Bosch-Removing_and_Replacing_Watervalve.pdf

http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

General 2008 troubleshoot manual I recently received from a fellow who got it through different company:
Shows parts and general parts diagrams start page 77
http://waterheatertimer.org/pdf/SVC810-Rheem-Ruud-Tankless-Service-manual-2008.pdf

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

You have Honeywell electronic gas control valve, and error code is 7 flashes.
Probably you have power vent model.
One manual from different company says: "Reset gas control using on-off button on front of control, replace flammable vapor sensor, replace gas control thermostat.
But with Rheem you also need specific steps: Remove gas burner and look for broken glass vial, and then blow out arrestor screen air intake using compressed air, clean burner parts, check for unobstructed venting, you will need new glass vial from Rheem depending on year and model number of water heater that appears on label on side of unit, or they may not have a repair kit for that model, and you might need a new gas control valve depending on model and how extensive problem was
You have Rheem water heater.http://waterheatertimer.org/How-to-repair-Rheem-FVIR.html
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
http://waterheatertimer.org/How-to-replace-thermocouple.html

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

According to the 2012 manual, 'the LED display only shows F.'
Bottom page 65. Yet the F temperatures are also shown as C in the manual.
http://waterheatertimer.org/pdf/How-to-set-Rheem-tankless-temperature.pdf
You probably have different model, or older model?.?
Older manual (page 15) shows same temperature range with both F and C, but typical of Rheem, the manual is totally vague about settings and say that qualified tech needed to adjust temps beyond factory default range (with no mention of display showing C) ... which is safeguard since the damg product cannot always heat water fast enough to reach higher set points above 120F.
http://waterheatertimer.org/pdf/TanklessOutdoor_95_84_64X_UC_AP15318.pdf

Call Rheem 800-432-8373 and give your product serial number and model number located on side of unit, and ask them.

Don't forget to keep the product maintained to avoid common error codes.
http://waterheatertimer.org/pdf/Rheem-CondensingTankless-maintenance-2012.pdf

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

I believe PTG2-42PVN is natural gas.
Rheem site does not show that model number.
As a general rule, Rhemm does not recommend converting NG to LP and LP to NG

Contact Rheem. 1-800-432-8373
http://www.rheem.com/products/tankless_water_heaters/customer_support/
http://www.rheem.com/products/tankless_water_heaters/
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

When having a problem with pilot and burner, the place to start is troubleshoot section in your manual.
Whirlpool is probably made by Craftmaster which I believe is a Rheem company, and Rheem makes a number of different models.
Some models have specific manuals and others have generic manuals.
Open Rheem water heater page and click on water that matches your water heater. On page that opens, click on tab that says 'specs' and then download manual.
http://www.rheem.com/Products/tank_water_heaters/gas_water_heaters

If none of those water heaters look like yours, open following link to help identify company website and download manual. Craftmaster website does not have instruction manuals.
http://waterheatertimer.org/Water-heater-manufacturers.html

All gas water heaters require periodic maintenance.
Some require yearly maintenance.
The burner parts require cleaning.
http://waterheatertimer.org/images/Clean-burner-300.jpg
http://waterheatertimer.org/images/Clean-burner-250.jpg
http://waterheatertimer.org/How-to-install-gas-water-heater.html

You can find age of water heater from serial number located on label on side of tank.
Label also shows tank size, and tank wattage and element wattage

http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html
http://waterheatertimer.org/Water-at-bottom-of-water-heater.html

Serial number decoder:
http://waterheatertimer.org/pdf/WaterHeaterSerialNumberDecoder.pdf
For example Rheem serial number 0790...
First 2 digits are month 07 July
Next two digits are year 1990

Rheem site does not show 81v40d
http://www.rheem.com/products/tank_water_heaters/electric_water_heaters/

I would say your water heater is from the fury series; new model number 82V52-2. I've included a link with my solution that you should take a look at. You could also look at water heaters of a different brand if this one isn't available in your area. Kenmore, GE, and Hotpoint are all very good brands of water heaters.

http://www.rheem.com/product.aspx?id=09DF2BDD-5E11-4D32-B574-84ACFB8A4619