Grundfos pump screeching

Having turned on the heating for the first time in a couple of months I was met with a screeching noise coming from our Grundfos domestic circulator.

Alll was working fine the last time we used the heating.

Can anyone suggest what to do? I am no plumber by any means and may need any suggestions spelt out in idiot terms!

Dan

This MAY sound daftb but if you can reach the center screw on the pump head undo it ,sorry , first isolate the pump valves with the power off then put some good washing up liquid into the shaft end and twist the shaft with an old small screwdriver,adding more washing liquid DONT use oil.turn the valves back on replace screw cap whe air stops coming out then turn power back on , it should settle down.