A kiwifruit vine that grows strongly, flowers every spring and never once sets fruit is not a sick vine. It's very likely the wrong sex, or the right sex with no partner nearby, and no amount of feeding or pruning will fix either problem.
Kiwifruit is dioecious, which is a step further than most home gardeners expect. A feijoa tree on its own will usually manage a light scattering of fruit because feijoa varieties are only partially self-fertile. A kiwifruit vine has no such fallback. Every individual vine carries only male flowers or only female flowers, never both, so a lone vine of either sex cannot pollinate itself under any circumstances. A female vine flowering alone in a garden with no male vine within roughly 6 to 8 metres will keep flowering, year after year, and keep producing nothing.
Every individual vine carries only male flowers or only female flowers, never both, so a lone vine of either sex cannot pollinate itself under any circumstances.
This is easy to end up with by accident, because kiwifruit vines don't show any visible difference between the sexes as young plants; the flowers that reveal it don't appear until the vine is old enough to bloom, which can be several years after planting. A gardener who buys one unlabelled vine, or two vines from an unclear batch that turn out to be the same sex, won't find out until the vine is mature and still isn't fruiting. Buying from a nursery that sells vines with the sex confirmed and labelled matters here, and it's worth doing at the same time as buying certified disease-free stock, since Psa, a serious bacterial canker, is a real risk with kiwifruit and both checks happen at the same purchase.
Even a correctly paired male and female vine can under-fruit if pollination itself is unreliable, and kiwifruit doesn't help itself here either. The flowers produce little nectar, so they're not strongly attractive to bees, and pollination can be patchy in a garden with low bee activity or a cool, wet flowering season. Home growers who want a more reliable crop often hand-pollinate, brushing pollen from an open male flower directly onto the stigma of a female flower with a small, soft brush, which is realistic to do on a home-garden scale since it's only a matter of a few dozen flowers rather than a commercial orchard's worth.
The scale of this crop is also worth planning for honestly before planting either vine. A kiwifruit vine wants full sun, needs roughly 4 metres of space, and grows into a genuinely large plant, up to around 3 metres of top growth on a vigorous permanent structure like a pergola or a strong wire frame, so retrofitting support after planting is much harder than installing it on day one. It's also a slow crop to prove itself: a first proper harvest is realistically 3 to 5 years away, and it's only once a pollinated female vine reaches full maturity that it produces anything close to the 20 to 40 kilograms a season it's capable of.
None of this shows up as a problem for years, since an unpollinated vine looks exactly as healthy as a well-paired one right up until the flowers fall and nothing follows. This site's premium check-ins are timed to a vine's actual flowering stage rather than a fixed calendar date, specifically so a missing male vine gets flagged while there's still a growing season ahead to plant one, not discovered again next autumn under a vine that flowered beautifully and fruited not at all.