Vokera Maxin 24 e - delayed ignition, radiator and hot water not working?

Hi, My Vokera 24e combi boiler is now tempermental as to when it will ignite. In the last couple of days I noticed it can take up to 3 hours before it ignites!!! In the past I have tried to set the pressure to 1.5 bars and in the past this would help to ignite but not anymore. What could be the problem for the extremely delayed ignition! Any help is greatly appreciated. Thanks