Had anything done recently, eg. Drained cylinder to change an element? Any alterations to the water system? Anything that would involve turning off the water in any way?
The reason I ask, is because it has worked for a year without fault, suddenly it stops. Something has changed... What?
My diagnosis from your description... It never worked properly from the start, but the element covered the fault by keeping the water hot, now the element is blown, or the ripple controller has gone bad and no power to the element, and the problem suddenly appears...

Or I might be wrong.