Trapped air is an indication of failed o-ring that separates incoming and out going water. This o-ring is located on the pre filter tray.
Usually if this o-ring is good, water enters the canister and the air inside will escape from the outlet gently. If this fails water enters the area below impeller directly and fills the entire pre filter tray making it difficult to let the flap open to allow the air to escape.
Verify the o-ring on the prefilter tray. If it is not above the little wall that oring sits in, then its the oring issue. If it is above the wall or you are sure oring is perfect and not causing this issue then you do as below...
When you clean the filter dont fill the canister with water, connect it to the line first and turn the adapter to on then take the outletand suck a little so as to start the flow once the canister starts to fill, wait until its completely filled during this time you can put back onto the tank, dont worry it will take some time to fill the canister and even any issue also water level reaches only to the tank water level, it wont flood your room if you hold the outlet in your hands...
Once you make sure the canister is filled, just turn on the power, within one or two min it will be air free.
I assume yours is 2080, it is the largest of eheims.
If the in-flow happens to be on only one intake and you see the second intake not sucking any water, just pinch the pipe that is with water so as to restrict the flow that pipe, so automatically canister sucks from the second pipe then you can release your fingures.
Update if you still have any problem
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