I had this problem and fixed it by fitting a new thermostat.

Update: I saw a fellow bongonaut in a car park in Colchester and asked him if he'd ever had this problem. He said that he hadn't but that he'd anticipated it. He used a product called "The Works" (10 quid from Wickes) to seal around the frame, so I took his recommendation and did the same. Problem ...

Thanks for the tips, both. The dealer is trying to find a professional auto glazier to do the job but without much luck - windscreen repair firms won't touch it. I reckon a sealer like this Sikaflex 512 will do the job, and I've seen it mentioned elsewhere as good stuff for sealing rooflights on ...

It has rained heavily for the first time since I acquired my Bongo a few weeks ago, and I've discovered that the window in the AFT roof is letting in some water. It's one of a catalogue of faults I've had with the van (that's a long story!) and I'm inclined to get the dealer to take it back. Before ...