The SL-X7-35 is the plainest and the cheapest of the Blue Sky instant heaters, and it is built that way on purpose. A flat square-edged case sits tight against the wall, and one recessed dial does everything — off, on, and the temperature between 30 and 55°C. There is no display and there are no lamps.

What it does not spend on the fascia it spends on the element: this is a stainless steel 3500W heater, the harder-wearing of the two constructions the SL series is built in. Water heats on the way through, heating starts at 1 litre a minute, and a thermal cut-out stops it at 60°C.

G1/2 connections, an 80cm lead and the supplied hanging plate mount it on a bathroom wall, and the shower handset, hose, inlet filter and flow valve come with it. Wire it on a 20A breaker with 2.5mm² cable from a 32A meter.