Are British Gas boiler engineers any good?

I had water leaking from the back of my boiler and had to have a plastic jug propped up until he got here to my home. He said I'd a 'burnt seal' and he fixed it. However, it is still leaking with water, in fact, even worse than before. I have had to call British Gas again and they're sending someone round today. I thought B.G. were good?