Posted: 21/04/2017 at 08:03
Some Hebes can die back if pruned too hard, and some don't recover from that. Do you mean large areas are fine, and it's only some areas that are brown? Has there been another shrub crowding them - that will cause brown , dead areas.
When the flowers die off, it leaves little brown 'sprouts' - but that's on the stem ends. It's best to prune those off to keep the plant tidy. Is it just that?
Too much wet at the roots isn't good either, so have they been waterlogged?
If you can upload a pic, that will help. Click the camera icon in the top right hand corner and follow the instructions.
Any other info you can offer will help too