FERROLLI DOMINA 80E PROBLEM STARTING IN THE COLD?

Boiler tries to start up fan goes,sparking ok, then makes a ocoilating noise and goes into red fault lock out this only happens when it cold ok during the summer.
I have changed the thirmisters if i keep running hot water and resetting it ,after about 10 times it fires up and i switch it to heating
please some one help me i,m a sparks out of work at the moment no money coming in .
Fitz