Boiler problem-increased pressure but now won't ignite?

Forget about pumping up expansion vessel you should only do that when boiler empty of water and to 1 bar pressure approx. One possible explanation is that your boiler has a flow switch that detects the flow of water round the system when pump comes on. If air was introduced into the boiler as a result of bleeding rads this flow switch would not pull on until air was released usually through automatic air vent on boiler or else by simply being pumped till it sits at the top of one of your radiators. If it is a combi boiler then some of these have bleed points that can be bled by trained personnel. But as you have found the problem usually sorts itself after a while.