Is it necessary to remove seed heads on fuchsias to keep them flowering?
Idealy ....Yes
I am feeding with a fuchsia food.
I get the feeling you are 'over feeding' assuming it is a liquid feed you are giving them.
What I am really saying is; you are perhaps watering them too much.
Fuchsias (a shrub) should be allowed to virtually dry out between waterings so if you are regularly liquid feeding you may not be allowing this to happen.
mine don't seem to flower as well this time of year
This could be down to what you did or did not do earlier on in the season, i.e. pinching out!
This is my slant on Fuchsia culture;
http://www.thegardenersalmanac.co.uk/Data/Fuchsia/Fuchsia.htm