Can you tell us if the wall is North south East or west facing? One of my very favourite clematis is Duchess of Albany. It is very vigorous and has small, pendulous, bright red flowers which bloom in late August right through until the autumn. Likes to be left alone until well established. I moved mine last year and am anxiously waiting to see if it flowers this year. If it does I will send a photo. It was on a South facing wall but now it is facing West.

A word of caution - how often do you prune back the ivy and at what time of year? Usually it needs doing twice a year, around May and then again in September, I find, so that means you have to be careful which clematis you choose, because you will inevitably cut it as well as the ivy when you need to, so choosing the right variety is crucial.

Things to remember about Clematis are. 1The like their head in the sun and feet in the shade. 2. They prefer a well drained alkaline soil. 3. They like a rich soil. 4. They should be planted so that the originial soil level is a good 3 inches or more below the new soil level. 5. They appreciate a good drink of water in dry times.
Given all that then there is no reason for them to fail, other than the perversity of plants.

the side of the wall that is planted is south facing,and edges my patio songthrush.As for pruning it Bamboo I haven't yet as it is only just starting to cover the wall .Boy isnt this gardening mind boggling trying to remember what needs doing when, Owdboggy I love the idea "no reason to fail" but wonder if thats really true!!!!Watch this space.
~Thanks Sheila

Note I did add 'except for the perversity of plants'. We have failed with a few Clematis over the years for no apparent reason.