Thanks for the replies. As I understand it, the PC should downclock the memory if it's unable to run at the maximum speed, not reject it. However, the single 8GB 1866Mhz stick shows as running at 1866Mhz, so I don't think the speed is the issue here. The memory is 1.35v DDR3L.
I'll have to buy some different memory to confirm.
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Update: I returned the RAM to the store and (whilst I was there) tried the NUC with an 8GB kit (2 x 4GB) instead. Specifically, Corsair CMSX8GX3M2B2133C11 (2133Mhz, DDR3L, 1.35V, Non-ECC). I choose the 2133 version as they didn't have the slower memory in stock and the price difference was negligible.
The 8GB kit works fine with both channels. The BIOS confirms that the RAM is running at 1867Mhz, which is fine. So, it looks like there's a compatibility issue with the 16GB 1866Mhz Corsair kit when running both channels.
I have very similar problem as original post (BIOS 0022). Two 4GB 1600 Kingston DDR3L work perfect, but 4GB 1.35v 1866 Crucial (Ballistix Sport) in "lower" slot causes power to flash three times repeatedly (works in "upper" slot only).
I did notice that Crucial seems to have twice as many chips as Kingston but wouldn't expect that to be concern below 16GB total. I've been using Intel boards for two decades and this seems like first time it won't accept higher speed rated memory (at lower speed).
Alex, I would recommend you using the correct memory on you system in order to avoid any problem on the future. If you are using higher memory speed, it could damage the processor. Remember that the correct memory speed supported by this NUC is 1600 and 1333 MHZ 1.35 V.
This link has additional information about memory features and the list of tested memory Intel� NUC Boards and Kits — System memory
Also, make sure you are running the latest BIOS available.
The following thread is about the same issue, you may check it out https://communities.intel.com/message/213308#213308
Thanks for your reply Sylvia, and I appreciate that you need to recommend the tested memory at the recommended speeds. However, the other thread you have linked related to using 1.5V RAM rather than 1.35V RAM. I have used 1.35V RAM throughout, so my original issue was not voltage related.
Nor am I concerned about the higher maximum speed of the RAM. The Corsair RAM is designed to run at various speeds up to the 2133Mhz maximum and the SPD table provides certified timings for operation at six different speeds between 1066Mhz and 2133Mhz. With the NUC, the BIOS automatically set the 1866 and 2133 RAM modules to run at 1866Mhz. I've run memtest at those settings and received no errors. There are numerous reports online (Google search) of this NUC working perfectly well with 8GB of DDR3L 1.35V 1866Mhz RAM from various manufacturers (Corsair/G-Skill/Kingston).
I'm still unsure why my original 16GB kit failed to run with both sticks when it would run fine with one. It would be beneficial if Intel tested Corsair/Kingston/Crucial RAM as the ones that have been tested are not widely available (at least in the UK).
Interesting article here::
When we set it (16GB) to run at 1866MHz in dual-channel mode the system would not post. We’d just get three blue blinks on the power button letting us know there was a memory error. We tried one module and it would run at 1866MHz in the slot farthest from the CPU, but failed to work in the slot closest to the processor/board. Intel is aware of the issue and hopes to release a BIOS that fixes the issue in the weeks ahead as they have Intel Ultrabooks with this CPU running just fine with 16GB kits at 1866MHz and 2133MHz.
Is a BIOS update upcoming to support higher speeds with 16GB?