Hi, depends on what you mean by low growing. There are penstemons that get to about 2ft tall, dwarf lobelia Fan series come in a gorgeous deep scarlet. but they dont flower all the summer but you should be able to get a range of plants that will give a procession of flowers. then you could go for some of the darker foliage of some of the heucheras.
cant think of anything else at the mo. sure some-one will help.

Lychnis vesuvius is a lovely perennial with very bright scarlet flowers and dark reddy/purple foliage too, grows 18-24inch won't flower all summer but will keep its lovely dark foliage, also potentillas are good only grow 12-15 inches tall and scramble around , flower for long time too if deadheaded regularly, I have monarchs velvet lovely dark velvety red flowers.

Try Dianthus, Spinfield Red, Geum, Mrs Bradshaw, Astilbe, Fanal or Glut.

Dianthus deltoides are about 12 inches tall and there are really good deep red versions of it. Very easy and evergreen foliage too.

Sounds as if this area is shady - Fuchsia Tom Thumb might be small enough if you don't want the height. And consider Seaburn's suggestion above of Heucheras - there are many varieties with varying coloured leaves, and quite a few have reddish purple leaves

Thank you all so much, I have looked at the plants you all have suggested and am trying to make a decision. I love the Geum, mrs bradshaw, I have one already so think it will be too tall, I have an octogan shaped fountain with four paths in the shape of a cross leading from it, and need vry low gowing edging to define the paths. pref no more them 8 inches, the garden is very sunny and dry with a little part in the shade.

Thanks

I assumed the area was shady because of the planting you'd already mentioned, i.e., busy lizzies! If you want something permanent there you won't find anything with vibrant red flowers which flowers all summer long except for annuals like busy lizzies (impatiens) but you could plant red leaved plants - have a look at Sempervivum, something like 'Othello' which has ruby red rosette type leaves, very low growing, or Sedums - 'Purpureum' has purple leaves, for instance. Both sempervivums and sedums are succulent type plants and tolerate drought very well, and like full sun, by and large.