16gb only reading 8gb it should read 16 in my sys right?

SBones

Honorable
Apr 24, 2013
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10,520
https://www.asus.com/us/Motherboards/SABERTOOTH_990FX_R20/HelpDesk_Manual/ an heres the manual im looking over now

asus sabertooth 990fx r2.0 mobo
windows 7 64 bit
gtx 970oc 4gb
Patriot Viper DDR 3 16 Gb Memory 2x8 GB Kit PC-15000 1866 MHZ PV316G186C0KGN
amd fx 8350 4ghz 8 core cpu just put in yesterday

I put in this patriot 16gb memory I got off ebay used to replace my 4gb .ther far left slot has always ben blocked by my cpu fan so I did slots 2 an 4(from the left) so the beige slots as used before,its only reading 8gb tho
it seems my mobo should support 32 gb?it boots ok so I assume its just reading one stick.i went back to my old 4gb's an they both read so the slot was nt damaged.next im trying a single stick,i assume that's all I can do an if one doesn't boot it must be a bad stick?