I have a Sombreuil and it generally blooms repeatedly throughout the summer, so I am suprised to here that your one is having problems since you have hot weather.

I brought my Sombreil climbing rose from Apuldram Roses, and it has grown very well.

Here is a link that might be useful: Climbing Roses

I second paulthor on Sombreuil's performance, it should be really good from the start, although it's not as profuse a bloomer as Climbing Iceberg. Iceberg on the other hand did not have much of a repeat after its major spring flush and instead invested in monsterous green growth from summer on (and had tons of BS, so I got rid of it). I think I bought my grafted Sombreuil from either Ashdown Roses (when they were still grafting their roses) or, more likely, from David Austin-US. They both usually deliver very good quality plants. I've also had good experience with J&P's roses, although I've only bought their own root new generation plants. You might have a weak plant there, so it may be an idea to get a new one (I'd recommend a grafted one) from David Austin.

Since I live in the UK now, it's interesting to hear that Apuldram can actually deliver good quality plants - all the (potted) rose I received from them last spring have been doing really poorly (they seemed to be awfully chopped in top growth and roots), especially compared to the ones I got from David Austin-UK which have done very well.

Andrea