Glowworm boiler ?

I have a Glowworm hxi condensing boiler which is 6 years old. 6 weeks ago it was making a continual noise that turned out to be the fan running at a slow speed but the boiler would not work. The slow fan was running without the boiler ignited and only stopped when the power to the boiler was turned off.
After 2 days the boiler worked again but then 2 days later the same happened.
The motherboard was checked for defects and was treated slightly however the boiler cut out again after 2 days.
All boiler wiring was checked for power and found to be ok
The boiler then showed fault code f3 indicating fan defect and a replacement fan was installed.
Again after 2 days use the boiler has cut out with this slow running fan noise continuing until the boiler is turned off.
My plumber has spoken to Glowworm who have not given any indication as to what the problem is.
We have reached a point where we either change the motherboard completely and risk wasting more money or go for a new boiler. Has anybody got any other ideas, good job its summer or we would have frozen.