We have a Rheem model 41V40-40F (mfg 11/2003) where the pilot light went out the other night. Re-lit, turned back on the burner fired and immediately went out.
Could not get the pilot to light again; waited ~ 10 & tried again, pilot lit and when turned on had a small KaBoom in the chamber from apparent gas build-up...
Figured I'm done and call the home warranty company (just bought the house 8 mos ago - home warranty provided w/ purchase).
Plumber that was dispatched tried was quick to access as an air flow problem with the heater (vent stack seams clear) and recommends a NEW unit.
My out of pocket after adding all the items NOT covered by the warranty is $470.00 for items such as:
$150 for permit (actual cost here is $65)
$90 for a pan (required for code even though we have no drain; what's new? ~ $15 retail?)
$50 for new gas valve (ball valve)
$45 for gas flex line (new looks excellent; don't mind new, but dang... $$$)
This company had a few negative reviews and honestly I feel they are possibly jumping the gun to replace as opposed to repair because they can get more money by replacing and adding all these other charges as opposed to repair

The owner has already admitted he makes his money on the mark-up of the parts not covered because the warranty company does not pay enough for the labor.
I'm all for making a profit; just feel this company is pushing the ethic limits (IMO).
Conclusion: I'm taking the 'cash out' option from the warranty company; my net after deductible, trip charge, and getting the plumbers 'net' for the heater is $175.00 - Oh Well...
I'm not a plumber but fairly handy. I can sweat joints and know how to 'properly' connect gas lines.
Anything in particular to troubleshoot as opposed to replacing entire unit?
I'm not against another 'respectable' plumber coming in but looking for input for DIY if an option.
BTW - we do have a second water that covers the dish washer, washer, and kids shower so we're not completely 'dead' in the water.
Sorry for the long post.
Thanks,
Steve