I have a rheem power vent ever clean hot water heater that shutting off and i have to reset it

1) Copy following links:
http://waterheatertimer.org/How-to-replace-thermocouple.html
http://waterheatertimer.org/How-to-repair-Rheem-TRD.html

2) GE is made by Rheem, so air intake screen is located below the combustion burner, as is the TRD (thermal reset device).

3) Modern gas water heaters, the FVIR, or FV system will trip when air intake gets clogged with dust.
This will slow venting of hot combustion gasses, except burner is still burning same amount of fuel. Overheating occurs, and that trips FV system.
Other brands require cleaning air intake screen and possible replacement of gas control valve, or FV sensor, etc. Each model is different.
Rheem_GE overheating will trip TRD, and glass vial breaks, causing air intake to close. Glass vial must be replaced, and possibly the gas control valve replaced.

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

Disproportionate number of water heater problems are Rheem-related, yet Rheem is just 1 of 3 major water heater manufacturers.

If you have Rheem tank-type gas water heater, and the combustion shut off has tripped the FV system, then there is a broken glass vial located under the burner.
Rheem does not post service manuals, and they may or may not send the glass vial for replacement. Depending on model which appears on label on side of tank. Year of manufacture are 3rd and 4th digits in serial number.
And they may want you to contact a qualified service technician (plumber)
You will have to replace glass vial, and clean the arrestor screen and clean the combustion parts, check gas pressure, and check venting.
Other companies post service manuals and do not rely on the glass vial.

Copy following links:
http://waterheatertimer.org/How-to-repair-Rheem-TRD.html
http://waterheatertimer.org/How-to-replace-thermocouple.html
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

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

Water heater brand, model number, type, location and approximate age are not known.
It is possible that water heater has tripped the FVIR system.
Water heaters manufactured last several years will shut down if exposed to flammable vapors, or high heat inside combustion chamber caused by inadequate air supply or clogged air intake, or bad venting.
Solutions range from replacing water heater, to cleaning air intake, to replacing-resetting TCO, replacing TRD glass vial, replacing gas control valve, installing louvers so more air gets to water heater, removing water heater from dusty environment, etc.
Other cause can be bad gas control valve, and possibly bad TCO, or tripped ECO requiring reset or replacement of gas control depending on specific brand and model number.
Review you product manual, look for identifying information on label on side of water heater.
Copy following links for basic troubleshooting:
http://waterheatertimer.org/How-to-repair-Rheem-FVIR.html
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

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

You're probably in for a service call and/or possibly water heater replacement if unit is more that 5-6 years old.
Your water heater plugs into outlet. Check outlet with cheap circuit analyzer to make sure the unit is receiving correct polarity without line interference.
If unit is in the attic, then add more venting to soffit and roof so pilot is not being snuffed out by hot air. If unit is in basement, then open some doors and a window and see if unit needs more air.
Most gas water heaters require yearly cleaning and service.
Clean the combustion parts and tubes.
Clean the air intake.
Have gas company check gas pressure.
Open following link for possible illustrations:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot

The problem can be bad gas control valve, air in gas line, low gas pressure, gas shut off handle not fully parallel with gas line, dirty combustion parts, lack of combustion air, improper venting. Or combination of all things. It's an electronic gizmo, anything can be bad or shorted, and repair may not last long.

Without a trained service technician to ohm-test the parts using correct service manual, then we are guessing at the cause.

Power vent water heater implies that you have side wall venting which must be replaced with another side-wall vented unit -or- it implies rapid reheating of water.

If water heater is more than 6 years old, you might be money ahead by installing a new one from local box store. Avoid the power vent and electronics. Local box store will have passive roof-venting type water heater BUT box store does not sell side-wall power vent. If your power vent goes up through the roof, then box-store variety gas water heater will work. Total cost $350 do-it-yourself for 40 gallon gas.
Or get 40 gallon 240Volt electric for $220 and connect to circuit breaker box. Requires no venting, and is easy to repair for years to come.
Or small 120Volt electric that plugs into outlet to tide you over until gas repairs can be made.
Look for scratch-n-dent models and always offer 10% off.
http://waterheatertimer.org/How-to-install-gas-water-heater.html
Shower uses 5-9 gallons hot water.

Rheem tankless do-it-yourself troubleshoot resources
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Similar 42vp50 direct vent product appears on following link:
http://www.rheem.com/product.aspx?id=C24E3F52-A6A4-4BC7-AF5B-0DF23A7A0263
sample manual for power vent series:
http://globalimageserver.com/fetchDocument.aspx?id=c0471d58-5e59-4be6-96f7-68361b8fb515

Manual has troubleshoot section:
If this is combustion-shut-off or FVIR or flammable vapor event, then manual says to call qualified technician.
Service call is certainly less expensive than any fire or injury caused by fire.
Other brands of water heater, for example Bradford White, have customer-resettable FVIR on some models.

Another thing that can be causing problems is air intake, especially in dirty environment like a shop, or if shop chemicals are being inhaled by burner. Burner parts are susceptible to chemicals in trace amounts below odor threshold. You might need fresh air intake for water heater, and air intake needs to be cleaned.

'System lockout' shows on troubleshoot page 32:
1. Gas supply is off or too low to operate.
2. Hot surface ignitor not positioned correctly.
3. Low voltage to the water heater.
4. Electric polarity to unit is incorrect - test and correct.
5. Combustion shut-off device tripped, contact service
agency.
Rheem phone number: 1-800-432-8373

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Fixya is always less expensive than a service call.

There could be blockage in your water heaters venting on the outside of the home. It sound like the high limit switch has been tripped. Try unplugging the tank and plugging it back in. this will reset the tank. if the problem persists you will want to call your provider for service.

if you have the exhaust run together it will not light up,, they have to be seperate,, the computer board sences the unburnt gasses and will not allow it to start,,

THERE IS RESETS ON THERMASTATS CHECK TO SEE IF THERE FLIPPED.