Hibiscus need several hours of direct sunlight daily and proper fertilization to bloom.
Make sure you're using a fertilizer that's low in phosphate (the middle number).
Also - How long have you owned the hibiscus and have they been pruned lately? Hibiscus branches that have been pruned typically take 3 months to regrow enough to bloom again.
Here's a website that have good info on hibiscus.
Good luck!
Barb

Here is a link that might be useful: hibiscus care

hi Barb,
thank you for your help.I was using a bloom booster fertilizer,which is 10-54-10.too much phosphate obviously.i have had the hibiscus 6 years.I have not pruned for over a year.I do believe it needs more light and might try it under some grow lights.

Hi Timothy

How did you make out with your indoor Hibiscus? Did it ever flower?

Thanks so much!