Filters will over time clog with dirt and grease until they no longer allow water to flow through. When this happens jets can feel less strong and heaters may cut out. On a regular basis it is important to thoroughly clean your filters.  For a deep cleaning you would remove the filter or filters from the spa and soak them for 24 hours in a bucket full of our white river cartridge cleaner and rinse thoroughly. This will chemically break down most blockages and resolve minor flow issues.