I plan to install a 450 liter accumulator in a loft in a victorian 4 bed detached house. I am worried about the weight. Should I get advice from a structural engineer before installing?

Yes!! With something like this the load displacement is crutial to the houses structural integrity.

Yes you should get advice as the joists in most lofts are only four inches deep. Jerry RT Plumbing

I would suggest that you get a structural engineer to advise if location of this needs additional supporting timbers. I would probably guess that it will need strengthening from previous experience. Bill Pipe Dreams Plumbing Services

Yes get a structural engineer to assess what you want however 450ltrs for a 4 bed detached sounds excessive to the extreme.