CDA 494 Dishwasher Error Cde?

Hi my CDA dishwasher has developed an error code (7 flashes). It has stood for many months unused,then used once two weeks ago, developed error, I cleared that by holding down start button, it then worked OK once. Tried again today and get error message again! Works on rinse cycle OK, but does not seem to want to heat water. Any ideas?

It's about five years old.

Many thanks

Gary
May 2009