The SL-X5-35D is the straightforward one in the Blue Sky instant range. There is no display and no menu: a single knob turns it on and sets the temperature anywhere between 30 and 55°C, and two lamps tell you what it is doing. That is the whole interface.

Water is heated on its way through a cast aluminium element, so there is no storage tank and no reheating between showers. The unit waits until flow reaches 1 litre a minute before it fires, and a thermal cut-out stops it at 60°C.

It mounts on the bathroom wall on the supplied plate, takes G1/2 connections, and comes with the shower handset, hose, inlet filter and flow valve in the box. Give it a 20A breaker on 2.5mm² cable from a meter rated 32A or more.