What type of expert could do that?

[Moomin12345]

Hi lovely people.

I've just started my first big renovation project. I'd like to knock down the wall between the kitchen and the dining room. This wall sounds hollow so it shouldn't be load bearing. I'd also like to convert the pantry adjacent to the understairs cupboard into a loo which will require creating a hole in the wall for a door and putting a wall in place of the pantry door as it's on the wrong side of the future loo. This wall appears to be load bearing.

Question to you - who is best positioned to determine if the said walls are load bearing and set out a way of doing all this safely? A structural engineer? An architect?

On that subject...

I've also got a tiny brick fire place that I'd like to have professionally sealed and a hot water tank in the guest bedroom that I'd like to remove as there also is a new combi boiler. Who could do these things? A brick layer and a plumber, respectively?

The hollow wall sounds like plasterboard. You Gould check they yourself by drilling some holes. For the door to the former pantry, if it is a brick wall it will be needing a lintel regardless.

Plasterboard / stud walls can be loadbearing so don't just assume that hollow = non structural.
You can check direction of joists above (are they bearing on the partition).
A decent builder may be able to advise but a structural engineer / architect / building surveyor has insurance you can fall back so if you're unsure i'd go down that route. They can also advise on required statutory consents.

Re the fireplace, you may need to include ventilation to the flue (at head, base or both) to avoid damp problems.
A plumber/heating engineer for the tank removal.
Good luck