There's more to a whirlpool or spa than pumps and electronics. There are in fact many other components. For example:
Overflow/drain with or without drain spigots for draining the air system and integrated water inlet in the handle.
Water and air massage nozzles
Most visible components are available in chrome-plated brass, polished brass or white - og chrome-plated plastic.
Automatic water filling:
17623020 Level Panel 230. For two sensors
20401310 Level sensor for spa, complete
20401910 Level sensor for equalizer tank
Dry run protection:
Detects whether there is water in the tub. Mounted on the outside of the tub.
17600020 Dry run protection 5 - 25V
Heat sensor:
17600520 Heat sensor 1/4"