Chilies not growing!! WHYY??

[creepycrawley]

Hi all.. I got a pair of chili plants here that are about a year and a half old, and they're only about three inches tall and haven't produced a single fruit, although they seem to flower with depressing regularity.. I shifted the plants away from my mint patch where they were earlier, wondering if they're stunting their growth or summin, and in the process I noticed their roots are rather thick, like a central tap root going a little to the side with only small to tiny branches on them... I asked my gardener about them and he said something about the roots getting too thick and being unable to produce fruit.. Can someone please help with this? I'm at my wits end and plus I've only just started gardening in earnest, so I have very little clue as to determine if the buggers really do have root trouble or something else... I have a load of theoretical knowledge on plant biology and pollination, but horribly little practical.. So, if someone can tell me where I'm going wrong and how to correct it, I'd be really grateful...

[SP8]

Not sure about the roots but I only ever keep one chilli plant going for 2 seasons maximum, planting out seeds from the biggest and best chillies harvested in subsequent years.

[pharmerphil]

What medium do you have them in?
Or, are these are planted outside, in the soil??

Usually a plant that sends out a single tap root, with no others is in soil that is too dense.
What do you fertilize with?

[creepycrawley]

Well they're both planted outside, soil has a tendency to be a little clayey, but is fairly good at retaining moisture on hot summer days.. Climate ranges from sunny to monsoon with cold winters, no frost or snow.. And for fertilisers I've switched to packaged compost quite recently, but have been using manure till date...