Vaillant F22 Problem?

Hi

I too have the F22 Vaillant problems and have read with interest advice and tips on what the problem is.

So I have a silly question (sorry) if the poor flow is caused by a blocked or weak pump, dirt or air or a blockage in the system, how can it be fixed? Do I get a Vaillant engineer in to fix the boiler, or water pump? Or contact the Green Sheild cover we have? Or some other specialist?

Sorry I did say it was a dumb question. I have just inherited this boiler.

Any advice greatfully received.

Thanks
Kim