The difference between them are:
Hoover FH50240 vs FH50230
images from manufacturer

Clean Surge:
The FH50240 feature CleanSurge whereas the FH50230 does not.
CleanSurge is a fingertip control that allows you to applly extra detergent to stains and heavy traffic areas.

Auto Rinse:
The FH50240 feature Auto Rinse whereas the FH50230 does not.
Auto Rinse helps cut your cleaning time.

Price:
The FH50230 is priced at $249.99 whereas the FH50240 is priced at $299.99 at hoover.com (prices checked on July 24, 2013).

Similarities:
Feature SpinScrub 77;
3 speed brush control;
come with SpinScrub Hand Tool, Squeegee Tool for hard floors, Upholstery Tool;
heated cleaning for faster dry time;
MaxExtract DualV Nozzle Technology;
carry 2 year limited warranty;
9 ft clear hose;
20 ft power cable;
10 amp motor;
SmartTanks System that allows you to individually fill, empty and rinse the tanks easily;
147 ounce clean water capacity;
feature Pressurized Edge-to-Edge Cleaning;

Download manuals to learn more:
FH50230 manual: http://hoover.com/file/646/
FH50240 manual: http://hoover.com/file/611/

If you know more difference between Hoover FH50230 and FH50240, please share here.