Follow the airflow path. Start at the nozzle, then hose, inlet, drum, filter and lid. A blockage or loaded filter can make a powerful vac feel almost dead.
1. Remove the hose and test the inlet
If suction is strong directly at the vac inlet but weak at the end of the hose, the problem is in the hose, wand or nozzle. That is a much cheaper problem than a motor.
2. Check for a partial blockage
A 2-1/2-inch hose can pass a lot of debris, but a rag, wood offcut or clump of leaves can lodge inside and catch everything behind it.
3. Look at the filter
Fine dust can coat the filter surface and restrict airflow. Clean or replace the filter according to the manufacturer instructions. Do not beat or wash a filter in a way the manufacturer does not approve.
4. Check the drum and float
Wet/dry vacs use a float mechanism to protect the motor from liquid. If the drum is full or the float is stuck in the shutoff position, suction can drop dramatically.
5. Check the lid seal and drain cap
Air leaks on the vacuum side reduce useful suction at the hose. Make sure the lid is seated and latched and the drain cap is secure if your vac has one.
If the vac is still weak with a clean path
If the hose is clear, filter is correct and clean, drum is empty, float moves normally and seals are good, the problem may be in the motor or impeller. That is the point to compare repair cost with replacement rather than buying more accessories on a guess.
The 60-second suction test
- Empty the drum.
- Remove the hose and test suction at the inlet.
- If strong, inspect the hose and accessories.
- If weak, inspect the filter and lid seal.
- Check that the float moves freely.
- Confirm the drain cap is sealed.
Fine dust is the sneaky culprit
A filter can look merely gray while enough pores are blocked to cut airflow badly. If the vac was used for drywall dust, sanding dust or fireplace ash that the manufacturer allows, filtration deserves special attention.
Accessory diameter can feel like lost power
Long narrow hoses and tiny adapters increase resistance. That does not necessarily mean something is wrong with the motor. Compare suction with the normal full-size hose before diagnosing the vacuum.
Sources used for this answer
Back to class: Wet/Dry Vac Class.