Heating cutting out after 20 mins ish

[Mrharkin]

Hi folks my central heating cuts out after 20 mins first of all to start the heating I have to press the reset button to fire it up rads get warm ish then cuts out I have both thermostats set to 30 I have bled all rads also I have noticedone that my expantion vessel in airing cupboard has no bar pressure at all this is and oil fired heating system

 

[joni os]

Difficult to be certain, from image, if red expansion vessel if off heating or hot water. Additional photos of expansion vessel and associated pipework might bring more response.