We have the most annoying problem on gas.Its the manuel spark one . I turn on the gas position and push dial in for 30+ seconds and push spark button several times and get sometimes a plop, other times nothing. Called in local tech guy and after turning on the hob which i have also done many times to purge the feed it worked. We arrived on site and it did not work even with the hobs alight.Thought i would turn on the gas boiler and lo and behold it worked. next time having done all the purging it did not work.Do you think i need a new ignition lead and new gas jet assemble or what. would be most grateful for advice .Thanks.