This "can and does" happen to DPFs with age. Yours lasted 14 years, I don't pretend to know if that's good or bad. When the computer senses that the DPF is getting clogged with soot, it sends fuel to a glow plug just upstream of the unit. The fuel ignites and burns the soot out of the DPF (I think it's called Regen), and the filter is good for another round. When the glow plug fails, the DPF clogs even more and the restriction of the exhaust makes the engine work harder and heat is the result. It's a bit like a catalytic converter (for a car) that can clean itself.
Sorry for your problem and glad it's fixed. Should be good for a long time !!