Well, it's sorted now, can't say I'm 100% sure what I fixed, but here's what
I did:

- turned off CH & HW inputs and boiler thermostat
- removed panel and boiler case
- gave everything a firm tap
- waggled the cables
- spun the plastic fan at the top left of the case
- restarted turned HW input on and boiler thermostat

The boiler went through the start up sequence and lit !! (wow, I ought to be
corgi registered huh?!)

What worried me was that the fan then came loose (like it took off
vertically) and landed on beside it's spindle. I powered it all off again,
pushed the fan on firmly, repeated the startup sequence and the fan spun and
remained in place.

Is this exposed fan linked to the fan LED? Perhaps it was this that got
jammed, hence it working loose.

James