High backpressure – what was the root cause in your case?

High backpressure is one of the most common HPLC alarms — and one of the most frustrating to diagnose, because the root cause can be almost anywhere in the flow path.
The usual suspects most of us work through:
— Partially blocked in-line filter or guard column (usually the first thing to swap)
— Column frit blockage from particulates or precipitated sample matrix
— Mobile phase precipitation — especially with high aqueous content or incompatible buffers
— Viscosity changes from incorrect solvent ratios or temperature
— Pump seal degradation introducing air or causing flow irregularities
— Blocked needle wash or sample loop on the autosampler side
The diagnostic approach matters a lot here. Isolating by disconnecting the column and measuring system pressure without it is a simple step that can immediately tell you whether the column is the source or not — but I’m surprised how often it’s skipped.
We actually built a structured High Backpressure Troubleshooter here on LabVeda that walks through ranked root-cause analysis if anyone wants a more systematic approach: https://labveda.com/tools-high-backpressure/
Questions for the community:
— What’s been the most surprising root cause of high backpressure you’ve encountered?
— Do you have a systematic diagnostic sequence you follow, or is it more trial and error?
— Any methods or matrices that are particularly prone to causing pressure issues?
Real case examples are especially welcome — the more specific the better.