Result of the harsh winter - some of them shoot from the base instead, others just give up altogether - you're not alone, thousands have died this year.

Mine survived the harsh winter and is producing three flower heads. It could be old age combined with harsh winter that's done yours in. A pity. Probably needs replacing.

a bit off topic but I have noticed loads of them flowering this year. Ours has flowered for the first times in about 8 years. whats the betting it dies this year?