Common problem is the rubbish diaphragm on these models. They're made of cheap material and wear away regularly.
Get someone to change this as this is the method used to heat water on demand, the diaphragm does not lift and make contacts meet, so new diaphragm (£15 I think) will sort it.
When the Heating is on a different heating method is used and the broken diaphragm is not used.
Golden
January 2011