I have a rheem 42v40 water heater which seems to have a combustion air supply problem. If you wait a period,(don't know exact time) pilot lights just fine but will go out after maybe 5 min. and will not relight until a period has passed. If thermostat is set for heating, after pilot is lit, burner will light but extinguish itself and the pilot within seconds and then the time has to be observed again before the same thing can be done again with the same results.I think it is a problem with the FVIR system. I am having trouble finding pictures of the guardian system components and their serviceability. Can the air shutoff be serviced?

I was informed by someone at Rheem that it may be the "safety sensor" that's the issue. My water heater is experiencing kind of the same thing. I can start the pilot, then shortly after it will go out. I have cleaned the thermal couple with some emery cloth, but not much help. I called Rheem, and they are sending me out the safety part with next day shipping. Free of cost, a one time deal.