Dont know what a combustion air switch looks like, where its located or how to fix one

1) What brand and model water heater?
Copy following link for troubleshoot by type of gas control valve.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

2) Clean air intake screen using compressed air or feather duster.
With AO Smith, craftmaster, state, reliance, american, kenmore, whirlpool, the air intake is located on bottom of heater. Rheem, richmond, ruud, GE, Bradford white, the air intake screen is located under combustion parts.
Water heaters today require plenty of fresh air. If air intake gets clogged with dust, then combustion byproduct moves up pipe too slowly for amount of fuel being burned, and this overheats combustion chamber.
http://www.thetankatwaterheaterrescue.com/forums/forum3/

3) Add a comment with more information

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

Look for an open ignitor or ignition switch. Have you seen this video:


If you need further help, reach me via phone at https://www.6ya.com/expert/dan_73bbd84fe1d95b61

Call Rheem
1-800-432-8373

TRD is flammable vapor system. Typically there is a glass bulb or fuse located in the combustion chamber.
See example image:
http://waterheatertimer.org/images/FV-TRD-glass-fuse-300.jpg

Remove the burner and look for the evidence of broken glass bulb that holds the air intake open.
Air intake is located bottom of combustion chamber, and bulb breaks causing metal plate to snap upwards and close off air supply to combustion chamber.
Rheem will have exact part number and possible instructions. Other people have wedged the air intake open to get system working again, but I do not know if that will work with your model water heater with electronic control. Working around the FV system exposes home and people to flammable vapor ignition and explosion when water heater is exposed to flammable vapors.
Example manual with illustrations.
http://waterheatertimer.org/pdf/Test-if-thermal-release-device-needs-replacement.pdf

Clean burner and pilot orifice and combustion chamber while burner parts are removed. Also clean air intake.
When burner is removed for cleaning, the access door gasket might need to be replaced.
Your product manual and/or Rheem will have that part number.

The flame rollout switch should be located in combustion chamber directly above the burners.Most of them have a red reset button in the center. Check to see if it will stay in when you push in on it. If not then replace it. Hope this helps you.Thank you.

sounds like you dont have a draft inducer motor operating or the controls for it arent working.

An un-vented heater should never smell like raw gas, you may get an odor of combustion by-products but never raw gas. If you are getting the raw gas smell you either have a gas leak or incomplete combustion. Always follow manufacturers operation instructions that state "open window 1/4" to allow combustion air" If the unit is brand new, you will get an odor for 20 minutes or so of oils burning off of the heater but that smell should go away. Do you have a Carbon monoxide detector in the house? You should!

Hi, new switch can be found on amazon... here: Amazon com Coleman air switch. I hope this was helpful. Cheers

I have 2 of these furnaces in mobile homes I own. On both of these the wheel inside the draft inducer blower that has the clear tube attached to it has a small wheel in it that over time tends to stick. Take the 4 screws out and give this little wheel located towards the bottom a push. Your problem may be solved without investing in expensive parts :)

Sounds to me like the furnace isn't getting enough fresh air for combustion and the pressure switch isn't closing. try taking the cover off the burner assembly and c if that works

Have you tried to replace pressure switch for the combustion air. If your not sure where to find it if you pull the front panels off follow the flue pipe down to combustion chamber the combustion fan motor is either inside the flue pipe or out side of it not sure on the one you have but you should see two plastic tubes that connect to a barb onto the topside of the fan and one on the bottom they both should go back to the pressure switch. i hope this helps you if you have any more question or if this doesnt fix the problem just reply back to this message . Make sure fan is working when furnace starts up. It should be the first thing that comes on when there is a call for heat