1. Open the purge valve on your pump.
   1. If the pressure drops, the high pressure is not in your pump.  Close the purge valve and let the pressure build again.  Go to step 2.
   2. If the pressure stays high, the most likely problem is the PTFE frit inside the Purge Valve.  See changing the PTFE frit document.  If the pressure is still high after changing the PTFE frit, the Purge valve should be replaced.
2. Remove your column from the system.  The column is the second most likely cause of the high pressure.
   1. If the pressure drops, the cause of the high pressure is either your column, or something behind the column.
      1. Replace the column with a zero-dead volume union.  If the pressure is still low, either replace or backflush your column.
      2. If the pressure stays high, go to step 3.
   2. If the pressure stays high, the cause of the high pressure is before the column, go to step 3.  
3. Start disconnecting tubing from the column forward in the flow path.  When the pressure drops, the last thing you disconnected is the cause of the high pressure.  Replace the part that is clogged.
4. If the Autosampler is the problem, switch to bypass and see if the pressure drops.
   1. If the pressure drops in By-pass, then the clog is in the needle, seat capillary, or rotor seal.  The most common place for a clog is in the seat capillary.  Try back flushing the seat capillary to resolve the clog before replacing the part.

If the above information does not resolve your issue, please utilize the Agilent Contact Us recommendations to request additional assistance.