Rheem Gas Water Heater Problem staying on?

[micro33]

I have a Rheen model 21PV40-1 gas water heater, which is relitivley new. Latley the water heater has been hit or miss at best. the electric igniter will heat up and a short time later the burner will ignite. The burner will run for a minute or two and then shut off. Within 3 to 4 minutes the cycle will start all over again. The vent is now running continually (past two days) and the vent in not obstructed. can you please advise what the problem could be!!
Thanks in advance!!
Al

[hj]

You could have any of a number of problems. The flame sensor could be bad. The vent air flow sensor could also do it if that is defective. Gas flow could be inadequate shutting off the burner's pressure switch. You should contact a Rheem service person, or else you may start replacing good items and waste a lot of money.

[master plumber mark]

Parts are free on your RHEEM water heater if it is less than 6 years old.

Labor might cost you a little.