providing heater plugs etc are working ok,and you say fault came on when filter was changed-i would start by checking all the filter seals,all 4 of them, did you change all of them (top and bottom seals are different size) are you sure they are not twisted? if all above is ok then it will possibly be filter head that is at fault- (i once had similar problem and it was found to be valves in filter head not closing due to rust under seats)
k
December 2007