Does Rheem water heater model # 72-40-1 have both electric and gas for water to be heated?

Any generic element will work.
Match wattage with current element.
http://waterheatertimer.org/How-to-replace-water-heater-element.html

http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html#parts

Rheem wants folks to buy parts from them... so Rheem tries to convince people that Rheem electric water heaters require special parts.
This is not true... ordinary generic parts will function fine on Rheem.

Gene

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

1) Electric:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

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

3) Rheem-richmond tankless
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

4) Add comment with information that appears on label located on side of water heater.

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

1) What kind of heater is it? Brand, type, approx age?
If it's a rheem-richmond-ruud-ecosense there are no service manuals:

2) Electric tank:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

3) Gas tank:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

4) Rheem Tankless gas. Sell it on ebay, and install gas tank for $385.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/How-to-install-gas-water-heater.html

5) Tankless electric: I have no resources.
6) Bosch tankless: go to their site and each model has troubleshoot resources.
7) Other brands tankless: I have no resources on hand.
8) Solar, boiler, hybrid, etc: I have no resources on hand. Search google with exact model and brand followed by .pdf to generate possible results.

9) Call manufacturer.

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

10-22-12
Copy following links to help identify product and download possible troubleshoot resources:

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

Tank-type electric:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

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

Other types of water heaters include boiler, tankless electric, indirect, solar-assisted, solar, hybrid electric, heat pump, wood-burning, gas hybrid, 3-phase commercial electric.

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

The power vent motor squeals when burner is activated?
See if you can oil the power vent motor.
http://waterheatertimer.org/images/Anode-under-blower-200.jpg

If the water heater squeals when water is turned on, then remove heat trap nipples and inserts and install di-electric nipples from water heater department local home store.

Copy following link illustrations.
http://waterheatertimer.org/Low-hot-water-pressure.html#trap

Additional link:
Troubleshoot by type of gas control valve:
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

GE is Rheem.
Models change frequently.
Copy following link for troubleshoot resources by type of gas control valve.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Newer water heaters require frequent air intake cleaning.
To do this with Rheem requires removal of combustion parts, and then air compressor to blow out screen.
It is probably time to have a plumber give water heater a catch-up on recommended maintained, such as checking gas pressure, bleeding gas line, checking vent draft, clean combustion parts, clean air intake, check if gas control is working correctly.

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

Open following links for water heater troubleshoot:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

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

Question posted under Rheem water heater.
Model number and gas valve are unknown. Add a comment.

Following information applies to typical tank-type gas water heater, and does not apply to tankless water heaters, boilers, indirect heaters, solar water heaters, etc or for electric water heater.

Electric water heater ECO is located on upper thermostat.
Open top cover and ECO can be reset by pushing in red reset button,
Or ECO can be replaced by replacing thermostat. Add a comment.

Open following link to see typical tank-type gas water heater ECOs:
http://waterheatertimer.org/images/Intellivent-ECO-900.jpg
http://waterheatertimer.org/images/Typical-gas-valve-500.jpg

The ECO will trip at 180-200 degrees F.
This happens when the thermostat fails, then the burner stays on, and the water will continue heating.

With most water heaters, the ECO is one-time use device and the gas control valve is replaced.
Some water heaters have resettable ECO, but the overheating problem has to be solved.
Each water heater is different.
Contact Rheem or read manual for correct procedure.

If you have intellivent gas control valve, open following links for typical service manual:
http://waterheatertimer.org/How-to-adjust-temperature-on-water-heater.html#intelli
http://waterheatertimer.org/pdf/Intellivent-service-manual.pdf

More resources:
http://waterheatertimer.org/How-to-install-gas-water-heater.html#troubleshoot

Rheem residential electric water heaters appear on following page:
http://www.rheem.com/products/tank_water_heaters/electric_water_heaters/

New water heaters are made with heat trap nipples pre-installed so the product meets industry energy standards.
Sample Rheem manual says: 'All models equipped with heat traps.'
http://globalimageserver.com/fetchDocument.aspx?id=052c9e32-ce37-48d7-8990-9e430f23fef3

Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

If it is an electric water heater, there is no pilot light. You could have bad elements or bad thermostats. Be careful working on an electric water heater, as most use 208-220 volts!

If it is a gas water heater, it could be a bad thermocouple, ignitor, gas valve.

My advice to you is to call a qualified service company to come repair your water heater.