A Fluval FX-6 refusing to start after being stored is fairly common, and it’s usually caused by one of a few predictable issues. These filters rely on priming, a clean impeller, and proper water flow to start—any disruption can make them act “dead.”

Here’s what commonly causes it and what to do:

✅ Most Common Reasons an FX-6 Won’t Start After Storage

1. The impeller is stuck or dried out

When stored dry, the ceramic impeller shaft or the magnet rotor can seize.
Dust, mineral film, or dried slime can “glue” the impeller in place.

✔ Fix:

1. Unplug the unit.
2. Open the lid and remove the impeller cover.
3. Pull out the impeller/rotor assembly.
4. Clean the well and the rotor with warm water.
5. Make sure the shaft is straight and the impeller spins freely.
6. Reassemble and restart.

2. The pump can’t prime because it’s full of air

If the filter was stored dry, the pump can have air pockets that prevent initial priming.

✔ Fix:

1. Fill the entire canister completely with water before closing it.
2. Make sure the hoses are already filled with water.
3. Plug it in—FX filters will self-prime every few minutes; give it 10–15 minutes.

3. Stiff or dried O-rings

The large black lid O-ring can dry out during storage, causing:

• Loss of suction
• Improper sealing
• Inability to prime

✔ Fix:

1. Remove the O-ring.
2. Inspect for cracks.
3. Apply silicone lubricant (do NOT use Vaseline).
4. Reseat it carefully.

If the O-ring is damaged, replacements are inexpensive and fix the issue immediately.

4. Debris in the motor head

Even small grit or calcium dust can block the magnetic rotor from spinning.

✔ Fix:

• Rinse motor housing and rotor cavity thoroughly.
• Use a cotton swab to clean the inside where the impeller sits.

5. Incorrect hose orientation or valve not fully open

FX-series filters won’t start properly if:

• Intake and output hoses are reversed
• AquaStop valves are partially closed

✔ Fix:

• Double-check flow direction (intake = 1 valve, output = the other).
• Make sure both valves are fully open and locked.

⭐ Is this common?

Yes—very.
FX-4/FX-6 filters frequently fail to restart after:

• Long-term storage
• Moving to a new house
• Sitting dry for weeks/months
• Being cleaned and left unused

99% of the time, it’s an impeller or priming issue, not a motor failure.

🔧 If it still won’t start

Try these last steps:

✔ Shake the canister side to side

Helps dislodge trapped air.

✔ Plug/unplug cycle

FX pumps restart their priming sequence every time you plug them in.

✔ Try spinning the impeller manually

With the motor head off, gently twist the impeller with your fingers.
If it’s stiff or gritty, that’s the problem.

✔ Replace the impeller

Impeller assemblies wear out or crack easily when they dry out.
If it hums but doesn’t spin → impeller is the culprit.

Replacement impellers usually solve non-starting FX-6 units.

🧠 Summary

Most likely causes:

• Stuck/dry impeller
• Air lock
• Dry O-ring
• Valves not open
• Debris in motor head

Fix is usually simple cleaning, lubrication, and water-filling.
Actual motor failure is rare..