my boiler keeps over heating?

my boiler keeps over heating and shuts of, also one or two of the radiators are off cold most of the time, now it cuts of after a few minutes of working, but the rest of the radiators get hot any way when the system decides to stay on. any ideas please? i thought of pump but as i said 5 of the radiators get hot befor the over heat so it couldn't be that !!!??? please

ash
February 2010