If I'm correct the S-Max uses a Fuel Vaporizer to inject fuel directly into the exhaust system to carry out DPF regenerations and this can fail/block so this could be what has happened on your car and is now causing your problems.
Below is a video for the Mondeo but most of the systems were the same between this and the S-Max.
Harsh, but likely fair. I'll need to be careful to give my "new" VRS a jolly good thrash in Sports Mode (the recommended way of clearing a DPF alert) at least once a month.
I was looking at 'new' cars similar to my Peugeot 308 when I bought it at three years old.
Got it for £6k, now £9k.
Mind you that was from an car leasing company so the difference could be nearer £1.5k using forecourt prices.