Glow-worm 60 FF Boiler Problem?

My boiler is 7 years old up until 3 months ago it was going fine but then started to make a loud droning/winding noise which wakes me in the night. Noise is coming from boiler not pump. After CH clicks in just 1 minute afterwards the fan is quite audible, loudly whirring then decending then becoming loud again. I have had the fan replaced (costly) but to no avail! Noise is quite loud. Also, thermostat switches heat off, but fan can be heard whirring/clicking again. Any suggestions please.