Glowworm Spacesaver Mark 2 gas boiler system prblem- not heating

My central heating and water not heating up . Gas boiler lights and fires up then shuts down before water and /or radiators get warm. Bled radiators and central heating pump. room thermostat appears to work -it clicks or raising and lowering adjustment.The grudfos water pump appears to work but could it still be faulty and not pumping through system hence boiler shuuting down? I have checked header and water supply tanks have water present in them. Any help would be most gratefully received

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.