How can I fix my potterton 80e boiler?

I did the paint work as diy. So I removed the one radiator from the bed room. since then boiler is not working. I thought because of the water flow or pressure . Now I done the paint work and put the radiator back on. Eventually when I switch on the boiler then it is start working for 1 or 2 minutes then switch it off . After 3 or 4 hours I can switch on the boiler same things happen again. I press the red button, reset doesn't work . I did air out from all radiators and boiler still the same. Before I can hear the water flow now I did not. Someone please advice me.