I have a plumber friend come and look at it. He is unfamiliar with this model of Vaillant. Anyway he found a drain nipple at the top and drained out a bucket of water there was according to him no air coming out with the water. Now on switching on the entire sytem is dead not a sound - no fan - nowt?
Clearly a lack of knowledge
The drain, more likely the vent nipple if that is the item I refer to, is located at a high point in the boiler to evacuate air from top of the boiler. Who in His right mind will remove a bucket of water when all that is required is purge a small amount of air
There are other drain nipples that will allow a fair amount of water to be drawn from the boiler with no sign of air
Gas had forgotten this boiler would have been your workload too besides likes of Bermudas, Ideal E Types to name a few. Cracking boiler, perhaps not as well made as the sine 18 for which I still have a heat exchanger ( will not get used now)