After a few uses the suction drops off. Tried washing the filter each time (takes days to dry). After three months there was no suction at all. Vax on-line help was no use. Finally managed to speak to a Vax person - I could return the machine, pay £60 and they would investigate. If they found the machine to be at fault, I would receive a replacement; if they found I had misused the machine, they would return it. I was not prepared to gamble £60 on Vax's investigation on top of the purchase price, and have junked it.
To update: I went into Currys to buy a new machine and seeing the Vax on the shelf remarked to the salesgirl the trouble we had had. She said Currys had not had any problems dealing with Vax. Being unable to decide on a new machine at the time, I called Vax again and received a totally different response: for a nominal administration fee of £3.99 they immediately sent a new machine. This is now working fine, though you have to be careful to look after the filter.