flashing ignition indicator on vaillant turbo max pro ?

i have been having a few problems with my vaillant turbomax pro

the heating and water works fine for a bit then the ignition indicator flashes
i have looked in the booklet that came with the boiler and it says a flashing indicator shows lack of water or poor water circulation in central heating system,

but the preasure gage reads a good 1.5-2bar


any help would be greatly welcome

thanks