Similar 42vp50 direct vent product appears on following link:
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
Rheem phone number: 1-800-432-8373
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.