potterton netaheat 16-22 not lighting probs?

I have just replaced all the rad valves in a mates house, drained the system, replaced all the velves and retreated the system but the boiler wont fire, it did initially but now won't light. I have bled the system so there is no air in it. also the pump inthe boiler itself is cycling I think as the bolier casing is hot but it hasn't even got a pilot light lit, as is the pump upstairs in the airing cupboard which apparently is an old problem as it is red hot but the pipes feeding it are cold.

I am not a plumber but do have a littlre knowledge , the heating part is set up with a Y plan. and I really don't have a clue as why the boiler won't fire.

An advice would be great

thanks steve