Onc. Twinkle and Gold Dust not flowering

[sweta]

Hi Orchid Pals,

Need some help with two of my miniature oncidiums Twinkle and Gold Dust that havent flowered since I got them about 3 years ago. I purchased them as mature plants that should have bloomed by now. Since I got them, I repotted them in small sized orchiata bark and they've grow couple of new pseudo bulbs, leaves and roots but no signs of flower spike. I fertilize them weekly during summer but once in 2 weeks during winter. They are grown under grow lights most of the time except for summer when I put them on the window sill. Our house temperature is 70F. I'm using tap water. I'm not sure what I'm doing wrong with these that they havent still bloomed. i live in the pacific northwest, seattle area.