I'd have thought there is a short maybe this is caused by leaking steam shorting the button. When you look through the guides you can see a 3 way junction..perhaps once the steam is redirected to frother then the steam is no longer shorting a connection. I'd take a look at one of the guides to open the barista and just have a look for evidence of a leak..debris/corrosion. You could try leaving the rear cover off and powering on the device to see the leak? Obviously you need to be pretty careful with personal safety and not go prodding around with metal screwdrivers or fingers.. we don't want a shock!