Trying to fix ideal classic boiler LXFF?

After taking out central heating pump and replacing some valves in the pipework the boiler refuses to light.I have followed instructions inside boiler, i am getting power to it and can here the on off swicth click into place but have no gas surge after over a minute. Got gas to come through once in over 20 goes, pilot lit but only lasted a short time. when the gas went off back to the same place, please help as getting cold and smelly