We've recently bought a property with an open flue, and we have had a rotating chimney cowl fitted to the pot on the roof. It was fitted by a property maintenance company that was doing various other jobs - replacing tiles, painting soffits etc. Today we had the chimney swept/checked and I was told that the cowl wasn't fitted correctly - there's a gap between the cowl and the chimney so it isn't forming the seal it needs to operate efficiently. I can see the gap from the ground, but I can't tell if it is due to poor fitting or if they've just installed the wrong size of cowl. I've emailed the builder and he insists it has been fitted correctly, but he's coming on Friday to fix some other snags so I've said I will show him the gap then.
Would it be reasonable to expect them to either fix it or replace it with a smaller cowl? They won't want to, because they'll have to put a scaffolding tower up again, so I'm bracing myself for a difficult conversation.