My ideal classic boiler is not operating correctly?

From cold the boiler runs for about 7 minutes, then is off for 1 minute, it then run on a continious cycle of 1 minute on and 1 minute off. I have check all radiators and the pump for air. No air in the system was found.
The boiler is set at heat 3 and the room thermostat is set at 22. This problem has only been aparent for a few days. What is the cause of this and how can it be corrected.