Like this:Good shout regards fan heater.
Pardon my ignorance but what's a tiled hatch and why is it preferable to siliconing the tile?
https://www.accesspanels.co.uk/tile-door-hinged/
I’m sure many other options available, but for housing association housing access hatches are a common spec item to get to isolation valves. In your case though you’d be looking at something more up market (like this) given the spec of the bathroom.