How can I lit a Myson 700C Marathon boiler?

I have just moved to a new house. Before I moved in, the main gas valve was switched off by the previous owner for safety. I followed the instructions to switch on the boiler. I managed to light the pilot but the boiler (Myson 700C Marathon) when I switch on heating/water clicks, and starts up like usual the pump works, but is not igniting (not lit through inspection hole) and does not heat the water and radiators. Could any one advise please?