Vaillant turbomax plus 824e tripping power?

hi all,

apologies for the lengh of this question/summary/

i have a vaillant turbomax plus 824e.

over night for some reason it knocked the mains power off, so i switched it back on and found the boiler kept tripping the mains......anyway i isolated the tripping to the fan in the bolier....which ive now replaced ( Wed 28 2008 ).

After replacing the fan i connected it all up and turned the mains on.....good news was the mains stayed on.....however after trying to fire up the light went to red and F.28 was displayed on the LCD, ive opened it again and double checked the connections on the fan and the circuit board......which for some reason has bought me back to the first issue.....the mains power keeps tripping :0(

what do i do now?

any help would be appreciated

Sam