By the way it sounds like you are describing a head flood. It can be caused by your magnets not gripping well - if so pry them out with a screw driver about 1/2mm.
Or it can be caused by your prints not sticking to the bed. Here is the fix for the second cause:
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gr5 2,224
Did you remove the filament from the top? Sometimes I still have the filament going into the core and forget you can't pull them out until you remove the filament first.
The whole head comes apart if necessary:
https://fbrc8.zendesk.com/hc/en-us/articles/115004541446-Printhead-Ultimaker-3-Ultimaker-3-Extended-
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