Have you tried asking on the citrus forum? The majority of my citrus fruit abort early on, especially when there's a lot of blooms, but they've always done that.

Um, good thought. I'll do that.

Maybe it just needs to have the soil changed. I imagine many years in the same pot would use up the nutrients in the soil even if its getting fertilizer or the soil could become very compacted after a long time. I do keep several citrus in pots like buddahs hand, all my diffent limes, lemons, grapefruits, pummelo and blood oranges in pots but keep the regular oranges and kumquats in the ground. Some of the larger ones I do not pot up anymore. My buddah's hand and thai limes are 8 feet now and I have to use a hand truck to get them around and even that is a pain lol. I do repot their soil every couple years or so though without going up to a larger pot. I root prune lots of trees beside just citrus and it doesn't seem to bother them too much. I have tall sausage trees that I prune off all thier roots every winter and shove them into tiny pots and keep them dry all winter.

Citrus will generally drop most of thier fruit or blossoms and only keep around 10% while they are young trees.

SJN, when you repot without going up a pot size, do you remove soil from the roots, and how far in to the rootball do you go? I've been trimming the tree back every year to keep it small. Not heightwise, as it has never gone above 4-4 1/2 feet, but widthwise. I'm quite sure the plant is rootbound, but sure don't want to wrestle with another big pot.

When I repot in the same pot I saw off the bottom third of the rootball and perhaps saw off some of the sides as well.
It sounds drastic but they love it.

I did repot, into the same pot, gave it new potting soil and scraped off an inch or more around the whole thing. Not as drastic as what you did, cearbhaill, but I'm watching it for a while to see how it does. It just keeps flowering, but the leaves appear to be less than perky.