i have a vokera linea max floor mounted boiler, have hot w but no heating?

i have a 12 year old vokera linea max floor mounted boiler, i am getting hot water(it runs hot for a while then cools down then returns to hot) , but no heating, the boiler fires up for a few seconds then turns of . the pump is running but no hot water is passing through, the flow pipe is only mildly warm close to boiler, there are no error codes showing.