I've had a climbing iceberg, up a sheltered wall for about 5 years, which always repeat flowers and looks glorious.

This year it's had blackspot (which I thought Iceberg's were immune to) and a distinct lack of growing leaves. It's still flowered well, a bit gappy flowering,rather than continuous so I've certainly had better from it. All I do is deadhead (and this year I've sprayed the blackspot), and give it a bit of fertiliser in spring. Can anyone please advise what I can do to gee it up a bit , prune it? replace it?- a bit difficult as under part of a patio.
thanks
Melanie