Water coming in through the flue

[caledonia1972]

Hoping someone can help - we have a Vokera boiler which is 5 years old. We have just had it repaired and when the boiler was opened up the engineer found that we have water coming in through the flue which had soaked the fan and some of the electrics.

We have been out on the roof and there are no obvious cracks or leaks in the flue pipe or the cap. Long term we are planning on replacing the boiler completely, but obviously don't want a hefty repair bill every time it rains!

Can we replace the flue cap with something bigger? Any other suggestions?