As I said I have fitted a a fair few of these, got one to fit in a couple of weeks, they are a reasonable boiler as boilers go, and Baxi seem to play ball on coming out on warranty stuff, but as I said, they do seem to be fokkers for air problems initially, I think I have had air problems on every one I have fitted, all fitted to the book pipework wise, pipes straight up, vent and feed arrangements, air separator, one I fitted was a low head arrangement, all to instructions, bloody thing wouldn't fill the boiler, disconnected the flow pipe at the boiler, nothing, had to cold connect mains to push the air out the boiler and get it to fill, it faffed around a couple of days and then settled, from my experience the Solo's seem to be like this.
Anyway, I sorted all of them at my own expense, but then I quote and charge a proper price for such eventualities, too many cheap merchants, so they ain't interested in coming back.
Not gas related so not a safety matter.