Each stick passes alone, the pair refuses to boot or crashes. This is a training and matching problem — here is the fix path.
Updated 11 Nov 2026 · 7 min read
Quick answer
When sticks work individually but not together, the pair cannot agree on shared settings: mismatched kits, an XMP/EXPO profile one stick cannot do, four-stick DDR5 training limits, or sticks in the wrong slots. Load BIOS defaults, use A2/B2, disable XMP/EXPO, and if they boot together at JEDEC speed, raise speed manually in small steps.
Contents
Why pairs fail when singles pass
Two sticks must share one clock, one voltage and one timing set per channel — and dual-channel interleaving adds its own training. A stick that is marginal at 3600 passes alone (single channel, lighter load) and fails when the controller drives two. Four sticks double the electrical load again, which is why 4×DDR5 at rated XMP speed is the hardest configuration on current platforms.
The fix sequence
- Slots A2 + B2. Confirm, don’t assume.
- Clear CMOS / load defaults. Boot the pair at JEDEC (DDR4 2133–2666, DDR5 4800).
- Stable? Enable XMP/EXPO. Unstable? Set speed manually 200–400 MT/s below the profile and retest.
- Still unstable? Raise DRAM voltage one small step (e.g. 1.35V → 1.37V DDR4) or loosen primary timings by +2 on CAS.
- Test with MemTest86, both sticks, 4 passes, after every change.
- Mixed kits that refuse all of the above: run them at the slower kit’s JEDEC profile, or replace with a matched kit — some IC combinations simply never train together on DDR5.
Buying your way out
If this is a new matched kit failing together at stock on the latest BIOS, return it — matched kits are sold as tested pairs, and yours isn’t behaving like one. If it is two separately bought sticks, the realistic fix is a proper 2-stick kit; resell the singles. See mixing sizes and mixing speeds for what usually does work.
Frequently asked questions
They boot together at 4800 but not at 6000 EXPO. Is something broken?
Probably not — that is a training/voltage margin issue, very common with 4 sticks or early BIOS versions. Update the BIOS, try 5800, or accept 5600: the real-world difference is a few percent.
Does stick order within A2/B2 matter?
With mismatched sticks, sometimes. Put the weaker/slower stick in A2 — training typically starts from that slot’s SPD.