Vaillant water heater

We (my daughter and I) have a Talbot Talisman Autosleeper GL which has been fitted with a Cascade II water heater, I would like to replace it with a Vaillant on demand gas water heater as fitted in the standard trim if possible, but am not having much luck finding one. I have been in touch with a seller on eBay, who calls himself "Talbot Parts Warehouse" says he has one from a Talisman that he is stripping that he says is working but he also says he cannot go into detail about it as he is not licensed to sell gas appliances. He is asking £200 for it with no guarantee or warranty, he will post it free of charge. £200 is a lot to pay for something with no warranty so I am going to explore other avenues. Does anyone know for one of these heaters?

I have to be careful in answering this, because one of this forum's members derides people for using Google to search for details that they can't recall fully, but...

The problem with the original Vaillant type of heater is that the burner flame is not isolated from the interior of the van - unlike more modern water heaters such as the Cascade where the burner airflow is completely external. This means that Vaillant won't comply with current regulations - it is not specifically unsafe, but it isn't intrinsically safe either, as it can lead to a significant risk of CO poisoning if it goes wrong.

That's (as I recall) the main reason for the Vaillant (and similar type) heaters ceasing to be produced.

I suspect that you would have difficulty finding someone to certify the install if you reinstated a Vaillant - though you may also find that there is no requirement to have it certified (unlike an install in a house, where it would be a legal requirement).

Having said that, if I had a choice between a Carver II and a Vaillant, I know which I would prefer to have - and it wouldn't be the Vaillant!