Worcester Greenstar 24Ri seems to have no power?

My Worcester Greenstar 24Ri boiler was working yesterday morning, but did not come on yesterday evening.

It is like is has no power. I'm sure the boiler is getting power. The programmer is fed from the same power source and it is working.

I've taken the housing off and checked fuse F1. This had blown. I replaced it and it has blown again.

What is likely to be wrong?