It turned out to be not a puncture, but a dodgy valve, which had begun to perish. The van had just had a set of tyres fitted all round, just before I bought it a few years ago and I assume that new valves were fitted too. The tyre bloke reckons though that many of these cheapo tyre places that offer a 'all in one' price are fitting the cheapest valves they can buy to save costs and this is the result
So, I've had 5 new good quality valves fitted, just to be on the safe side. It might be worth checking the ones on your vans in case they are cheapo ones
