My engineer just came around. Not particularly friendly or helpful, no smile, came in like he was doing me a massive favour. Hate people like that.

As it happens though, the problem was a small microfibre cloth stuck in the pump! So I guess
technically not a warranty issue. Nevertheless he said it's the most common callout thing.
So pull the flap open at the front and see if you can find anything blocking the hole.
I think the lesson is, don't put any items in the machine that are too small.