firebird

Hi thanks in advance fire any help. My 20 year old firebird 90 boiler has run really well with only one control box and one photo cell changed 3 years ago. 3 weeks ago it started to flame out when trying to ignite when hot so I decided it needed its first proper service as I have done it...

Firebird boiler isn't firing so I assume I need to bleed it, but I'm not sure where the valve is. I keep seeing different things online that say I should loosen the valve where the Allen key is, or the lower hexagonal nut. Which is it?