What could cause a blockage in the drain hose leading to error code F9?

Blockages in the drain hose can arise from various sources, including lint, small objects (coins, buttons), hair, or detergent buildup. The hose should be inspected regularly and detached from the drainpipe to check for obstructions. Using a flexible brush or water jet can help remove blockages. Ensure the hose isn't kinked or crushed, as this can also impede drainage.