My richmond model # 5v40s won't keep heating - Audiovox Richmond 6G40-36F 6-Year Tall Gas Water Heater

Could be the thermostat is faulty or perhaps the heating element has developed a fault that is overloading and causing something to keep tripping out.

If the heater is modern it could have electronics that are causing problems.

The most common heating elements in an electric wtr htr are 120v 4500 watt elements. There are usually two of them. The bottom element heats about 80% of the water, and the top one heats the remaining 20% after the bottom stat is satisfied. The info you are looking for is on the rating plate of the heater. Good luck!

Flame sensor needs cleaning ??

Richmond 40-Gallon 6-Year 4,500-Watt Medium Residential Electric Water Heater # ...Double 4500 watt heating elements for faster recovery

Check the thermocouple and the control box.

Tom W must have been 'recommended answer' from past answers, and not live answer.
What did Tom's answer say?
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

Electric water heater is fully repairable unless it is rusted out.
All 2-element tanks are 240Volts.

If you have NO hot water, then suspects are 240Volt circuit supplying only 120V, reset button is tripped out on upper thermostat, bad upper thermostat, bad upper element.
If elements were not completely covered with water when power was turned on, then elements will instantly burn out.
When filling water heater tanks, open bathtub spout. Wait for water to come out full stream. Then open TP valve on water heater for a moment to remove last of air. Then turn on electricity.

Open following link for complete troubleshoot walk-thru.
http://waterheatertimer.org/How-to-troubleshoot-electric-water-heater.html

resetting your lock out for richmond power vent

Now change the thermostats........this is the only other thing it could possibly be.