Below are the most common causes for this problem and the remedies for each:

Pool water level too low

Top up pool

Hair & Lint Pot clogged

Clean out basket

Hair & Lint Pot lid o’ring

May be warn / damaged or missing - replace

Skimmer flap jamming

Adjust or replace flap and or hinges

Leaks/loose fittings in suction line

Repair or replace

Leaks in pump

Repair

Filter not backwashed
(Can test system by running on
bypass or removing cartridge/s)

Backwash or clean/replace cartridge/s

Blockage in inlet pipe

Pressure test and remove blockage if possible

If only when vacuuming:

Has vacuum hose been 'bled' first
(i.e. filled with water)

Fill hose with water

Hole/s in vacuum hose

Replace hose