Clematis are funny things - down the years, I've known two that 'died' and didn't regrow, but in both cases, when I went to replant, I found the roots of both - they still looked healthy, so I just added some composted manure around the roots, covered them back up and hey presto, they both grew again. But I've also had more than a couple of young clematis that just gave up the ghost in the first year...Clematis roots are usually fairly thick and quite yellowish, if you fancy digging around carefully to see what's there... assuming you planted into the ground, not in a pot.

Hi, it could also be planted in a rain shadow, as it's on a trellis, I presume this is atop a fence, which may be preventing rainwater from reaching the root of the Clematis, if it's planted right up to the fence, try planting it further out from the fence, and angle the plant toward the fence, but as Bamboo says, have a look for the roots, if they're dry and dead, you will need to replace the plant, Derek.

is there any run off that may have chemicals in it that could be the cause.
if not then perhaps just to dry as suggested.