Question Dual Channel (Channel B) not working?

May 9, 2023
Hello, im new to building computers and am currently tinkering with a build where only ram sticks in Channel A seems to let the system post. Hoping that someone would be able to help me get to the bottom of this problem!
I am using the following:

CPU: Ryzen 5 3600x + wraith stealth cooler
RAM: Corsair Dominator Platinum RGB 32GB (4x8gb) DDR4 3000mhz c15 kit (sku: cmt32gx4m4c3000c15)
MOBO: ASUS Tuf Gaming B550M-Plus

When i power on the system with one RAM stick in A1 slot or A2 slot, the system will post and enter bios or windows. It will also post by filling both A1 and A2 slots simultaneously.
However when i put a stick into B1 or B2, the system will not post and the Debug led stays on DRAM and nothing will happen.
I have tried all different combinations of using 1, 2, 3, 4 sticks and in different slots, however the system will not post if there is a stick present in the B channel DIMMs.
I've updated the BIOS to the most current for Windows 10.
The RAM is on the motherboard QVL.
I've tried RAM from my main computer in this motherboard which works the same as above (posts in Channel A but not when in Channel B).
I've removed the CPU fan, reseated the CPU, reapplied paste and reinstalled fan. I tightened the CPU fan screws until they were fully in, but not overtightened. I had a look for bent CPU pins and i think it looked fine..? Blew the socket out with canned air and did the ram slots while I was at it. The CPU fan however is running around 2200-2400 RPM with the system just idling, which i think is very high? It also makes a whining noise when i power down the system. CPU temp sits around 45-49 degrees celcius while idling.

Any help and suggestions are welcome!
It is quite safe to assume it's not faulty RAM. So what's left is either faulty CPU or motherboard or cooler too tight. The last option is easy to check - rotate case so motherboard is flat and remove cooler screws (so it's only held by paste and gravity), then check the B slots again. Unfortunately there is no way to tell if the problem lies in CPU or motherboard without trying spare parts, and as both are second hand the chance is like 50/50.