Need advice - LC 20AB pump question

[odonal01]

I am using a Shimadzu LC20AB pump and it is not correctly pumping the methanol phase through the system. I have cleaned the check valves and pumped the system so as to removed any air bubbles but nothing has seemed to work. The soluble phases are located above the pumps and when purging the system no issues arise. When trying to run the pump at the desire flow rate the pump reaches a max pressure and an error message occurs. Any help would be great appreciated.

[nk1124]

Is there another solvent currently on the system? If theres water on the system methanol water mixtures create pretty high backpressures, if so perhaps try to run methanol at a lower flow rate for a while until the pressure drops and you can return to the desired rate. Is this only for methanol or other mobile phases as well?

[odonal01]

The system currently only operates with water and methanol. I have run the system currently at a low flow rate and the pressure has not returned to normal so I am unsure as to what to do.

[unmgvar]

since you are having a max pressure problem, air bubbles are not relevant here.
something is stuck in your system, you need to find which part.
the idea is to go backward from the detector back to the pump each time disconnecting a connection or tubing away.

but here are the most leading suspects by order of most to least:
your guard if you use one
your column
the filter frit at the head of the pump
injection port
the needle
the injection valve