Fluval 406 Troubleshooting ( many models apply )

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Aquarium Advice Newbie
Nov 24, 2022
Ok first off I'd like to tip my hat to all the great advice here.
Thank you for the welcome.
If this belongs elsewhere , my bad.
So I bought a used Fluval 406 and hoped it was going to be plug and play. Nope.
Hard time priming and then finally just force fed the intake. Voila!
But then it would only work intermittently(sp). Quite noisy as well.
Took it all apart to discover that the impeller was at fault and the ceramic shaft that stabalises it was missing.
Ordered new impeller which comes with shaft. $20 Amazon
Turned unit on and it worked, sorta , now to discover that main head gasket leaked. And we all know that aint gonna cut it.
Removed seal , cleaned it well , then before re-installing I wrapped a wide elastic band around the head where the seal goes ( to take up any gap) then installed seal.
Seemed to do the trick , fired up unit to now discover that the " aqua stop valve " also leaked. Could audibly hear it.
Figured out how to disassemble aqua stop valve to inspect. All looked good but obviously it wasn't. Removed seals from either side of shaft , smothered them in vaseline and re-installed. Voila! It ran great! Except for a tiny tiny leak , but that wasnt good enough for me so I took it apart once more and in doing so I broke one of the seals dagnabit!
I ordered new aqua stop valve $24 Amazon, installed and it runs as new now.
Thought I'd share my experience, hope it helps.
Included is some pics of the valve disassembled and the gasket that I broke.

As a side note: I think the gasket problem most likely was due to the canister being used previously on a salt water set up and then once removed it sat and dried out considerably.


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Good post. I wound up replacing both the impeller & motor. Used F4, the big one that looks like a shop vac
Hi and welcome to the forum :)

What a wonderful introduction you had to Fluval filters :)

I miss the old style filters, they were so much simpler and rarely had issues like the new ones do.

The priming devices on new filters are a waste of time and always cause problems, regardless of brand.

Good that you got it going though :)
I find my 406 rattles after a year or so. Get the maintenance kit and replace the impeller, impeller shaft, impeller cap and o ring every 12 months.

There are 2 versions of the 406 also. Yours looks like the later version. A lot of the parts are different for older 406s than newer so make sure you get correct parts. The aquastop valve from older 406s doesnt fit the newer 406s for instance.

I think the earlier 406 took a lot of parts from the 405, and they updated the filter to use different parts midway through its run before they discontinued it for the 407.
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What old style, Colin?

Early Fluval external canister filters (like the Fluval 303) were round and had one o-ring. That was it. No fiddly primers or weird shaped seals, just one o-ring that fitted between the motor and case. They ran a stainless steel impellor shaft and the whole unit lasted for years.

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