Hi! I have a problem Hi! I have a problem with an oil heating system! When I turn it on, it heat

Question

Hi! I have a problem with an oil heating system! When I turn it on, it heat for 5 mins then stops. I have changed out the circulation pump as I thought that this was the problem. The pipes in the boiler are warm. The heat doesn't go to the radiators around the house. I Found that only 1 radiator heats upstairs. There is water in the radiators and none are air locked as i have tried them all.