Interestingly enough....I just did a complete cleaning as well as a crash course on how its made and what makes it tick on my Pentair minimax plus 400. Its fresh in my mind and I hope I can help ease any anxiety or questions you might have?
First of all, don't let this lil hotbox intimidate you, There really isn't much to um? It sounds like you already have a feel for the task at hand.
As far as cleaning? you will be on your back for this job.
I had 2 burners that weren't working at optimum, come to find out spiders had built a minimall in 2 of the burner nozzle's.
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So i recommend removing each nozzle when disassembling burner assembly. this was probably the hardest part of job,they can be stubborn so make sure you use a tubing wrench when first breaking them loose, to avoid stripping or rounding off nozzle's. once you break them loose you can use a a regular or ratchet wrench to complete the removal/reinstalling process. a simple inspection with your eye is all thats needed its a pretty big hole in nozzle so if clogged a mini flat screwdriver will do the trick.
As far as burner assbly, your right it can be a little tricky, you'll have to remove igniter which is fastened to burner by 1 phillips head screw.
Then just sort of pull the feeder line(the piece of tubing that has all nozzles attached to it)out & up towards you, being careful not to be to hard on it, you only need to move it maybe 1/4" to free up burners, infact a few will will actually fall out, not to worry? you will be removing all of them anyway so, once you have burner out you'll notice each one has a little hook on the end, think of it as the hanger, cause thats all that holds them up, that hanger slips in to a slot at the back of heater, then the front part of burner is hung over the nozzle itself. I found my burners to be in good condition, I thought i would have to ream some of the holes but that wasn't the case.
Like I said assembly can be tricky, just be patient, eventually you'll get most of the burners to cooperate and stay in position. its ok if a couple aren't seated correctly, you can fine tune after you have turned feeder tube back down to its original position. when it's right? all burners will looked uniform (equal distance between each etc.)
PS there are four bolts that hold burner tray, these will test your wherewithal for sure. As well as make that beer taste so much better upon completion.
Good Luck