HI, how can I fix my Veissmann vitodens 100 ?

The 'infamous F5' fault has popped into the window and a red flashing light with no heating or hot water. I have taken the front cover off to look for the fan that has been mentioned before to try to use the hairdryer method. However, I cannot see a fan - just a huge metal drum (a bit like a washing machine. Are we talking at the back of the controls?