A clothes press is just a cupboard for keeping clothes in, Uncle. A *hot*press, on the other hand, is a specialised cupboard, containing the immersion (yes, the water heater - a copper boiler with an electrical element immersed in it, like an electric kettle's), and above that, shelves made of 1" by 1.5" slats with 1" gaps between them, so the clothes and linen can be kept dry and warm. Usually they have louvred doors to allow passage of air in and out, but not always.

The pictures were some of the ones I'd found, but I've found none that actually shows the whole thing - the immersion at the bottom, and the shelves full of folded clothes and linen above it.