Errors with shimadzu pump LC 20AT

[Eliford]

Dear Forum members
We have a situation and hope you can assist us.
Our pump Shimadzu LC20AT has become strange. It was left running at 0.2ml/min flow rate of methanol/water(50:50) for a long time. One day we found it beeping the error being P-MAX. Despite disconnecting the column and guard column, the problem persisted. Despite ultra wave sonnication of the check valves and flow line filter, the problem persisted. Despite removing the right and left plunger (piston) head, washing the seal holder ASSY, inspecting the plunger seal and cleaning the piston(plunger) and reassembling, the problem has persisted.
The pump pressure is always reading 759kgf and Max pressure is 300 MPA even when you restart it. When you turn it on it will be like that, some times pressure may fluctuate between 0 - 759kgf. When drain value is opened and purge button is pressed it doesn't purge but an error reading says "open drain valve"
When pump button is pressed with drain valve open, it doesn't pump but an error reading says "Maxim pressure exceeded".
Some time even without any noticeable leak there is a error display for "ERROR LEAK", some times there is a "DEGAS ERROR".
The errors are becoming unpredictable and the users manual for troubleshooting is not helpful.
What might the problem and how can we resolve this?
Best regards
Eliford

[DR]

It's probably a messed up pressure transducer and/or pulse dampening assembly.

A service call is probably not a bad idea, or send it in to get it sorted out. If you're mechanically inclined, you may be able to remove and test those items yourself if you are provided with a little guidance from a friendly SSI field service engineer. Or send them in to be tested if they allow that.