Fluval 405: impeller cover pops up. Persistent


New Member
Apr 30, 2021
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The impeller cover keeps popping up on our Fluval 405. It has been a persistent problem for years. I showed the problem to Hagen but they were unable to help.

The initial observable's are: noisy filter, a cover that has popped up every time I clean the filter, and significantly reduced flow.

I diagnosed the problem myself, with no analytical equipment, so I may have missed something. Fluval customer care had never seen the problem and had no solution.

Analysis: the impeller creates high pressure that drives the filter, so the cover can only pop up as a result of pressure from the impeller. Next, lets look at what holds the cover in place.

Inspection of the seat of the impeller cover:
The seat and clips are fine - no bent or worn edges, and nothing obstructing the cover. However, on the filter head, the part that the cover clips into (the female part) has bent.

High pressure in the impeller bent the female part of the cover clip on the filter head.

Perhaps I overfilled the carbon causing the back pressure to spike, benting the female part of the cover clip.

Watch state. Reducing the medium, checking the bent part and will see if the problem is resolved.

Has anyone else had a similar problem resolved?


Fish Guru
Jan 26, 2008
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Perth, WA
Post pictures.

The impellor shaft could be the wrong type and might be too long.
The rubber grommets on the ends of the impellor shaft might not be on all the way.

Take it to the place you bought it from and get them to check it and compare it to a new one.