The radiators won't heat up?

The pilot light on the gas central heating is lit but when you press the button that gets the radiators to heat up, nothing happens. It should light up lots of burners which you can see through a spy hole, but they're not lighting up. The gas bottle outside is connected and full. It should be fine. The make is Stelrad Group - Ideal Elite - Propane Gas Boiler. The controls/timer is a Myson Microtimer 7. It was checked by a qualified person about 6 weeks ago. Today when I put the radiators on it lit up for a short while but then went out. I tried more times but it won't work. What should I do?