How long have you had the plant? Does it get bright light, and what do you feed it with?

Thank you for your response, I have had it 15 years it is in the bathroom and I do not feed it, is that the problem. I have grown two more plants from it one I have on the office windowsill and I feed it Baby Bio but they are only 6 months old.

Hoya needs the following:
Average warmth, but keep cool in winter (50-55 deg F) in winter
Bright light with some direct sun
regular misting, except when in bloom
Do not disturb the plant once buds appear
Do not remove dead flowers
Do not repot until unavoidable.

I asked what you fed it because a high nitrogen feed is great for the leaves, but might discourage flowering if over used. Check the conditions you're keeping the plant in, do they meet the criteria above?
If all else fails, give it a shot or two of tomato food in late February/early March to encourage it.