Could be Raj.
There should be a fault diagnosis chart on the inside of the front cover. I'm assuming you've followed it and its told you to replace the fan.
before proceeding does the "HWDEM" LED light when you turn on the hot tap? (It should!)
Can you hear the fan turning? If so then its unlikely to be the problem
If you need to get to the little bugger:
Its is at the top of the unit, Its been about 6 years since I did this but I remember its relatively easy to get to. Take it out (remove all power before doing ANYTHING!) and see if it will turn VERY easily and keep turning. If not it does need replacing.
Its a relatively easy job for the DIY geezer but if you have ANY concerns I'd call in a plumber to do it.
A new one costs between £60 - £100ish and a plumber would probably add another £50 - £100 on top to do the work.
Riggsy
October 2007