Falling buds on Hibiscus plant

I have a  large hibiscus which has formed hundreds of buds for years since planting but they turn yellow at the base and then fall off. Hence, the plant has never flowered. Can anyone tell me why this might be happening.I've tried regular watering, cutting it right back one year and feeding it. I'm on the point of getting rid of it.  Grateful for any help. Thanks.