I see many reports in the forums of Adblue problems caused by crystallisation that normally require expensive replacement of tanks/pumps/sensors etc. As a chemist and a chemical enginner I know that the main component of the stuff is urea which is very easily soluble in water, so in principle  it should be simple to clear any blockage by flushing with water. Has anybody tried to do such a thing? I realise it would need some sort of electronic interface to the car to force open valves and run the pump and so on. That sort electrickery is well beyond my competence, and as my A3 predates Adblue I have no experience of it, hence my question here.

Not aware of a flush as such. The injector before the catalytic converter is prone to crystallisation. It can be cleaned with warm water and a little vinegar and a little nylon brush.

There are a number of additives on the market, but your guess is as good as mine regards their claim to reduce crystallisation.

VAG AdBlue is part number G052910M4.The Issue is more complex, in the respect of what VAG engineers were trying to achieve by reducing Euro 6 diesel emissions with DPF, EGR and AdBlue in conjunction with a catalytic converter.

To be honest Euro 5 technology was fine and dandy, but with low emission zones in cities, then you risk a congestion charge if you enter, which is entirely possible if you don’t know the city, or hit roadworks that could detour you.

Driving style is important too. Diesels like to get up to temperature, so start stop short trips will likely cause issues down the line.

Just my tuppence worth.