how to replace the steam switch?

The manufacturer Morphy Richards sell appliances - they may indeed sell some spares to domestic appliance spare parts companies but I doubt they deal directly to the public.

My experience is that irons are generally not made these days to be repairable - you have to destroy an iron to get inside it so even if you could find the switch you seek you'd have a difficult job making a repair.

Furthermore - it may or may not be the switch itself that's causing your lack of steam - the element that makes the steam might be defective.

Notwithstanding a defective element or broken steam switch the iron might be suffering from an internal build up of calcium so badly that the steam is prevented from escaping - an artery blocked or the switch seized perhaps. A solution of citric acid powder left in the iron overnight might dissolve any contamination - but that's the least likely cause in my opinion.

My advice is to give up and invest in a new iron - one less complicated and much cheaper.

Good Luck...
March 2017