home heating popular 90 boiler ?

My boiler will start up but after a short period of time about 4 to 5 mins it goes off and will not start again for about 30 mins, i have tried to start it with the pump turned off ans same story and i turned off all the rads in the house as i read online to do this and turn one on at a time etc but again same result the boiler turned off again and the red light is gone off. I also did bleed each rad with the key and let out all the air multiple times. Thinking it might be the thermostat but could be wrong.. Any suggestions greatly appreciated.