Ravensheat. Have changed diverter valve now boiler wont fire at all?

Please help, pulling hair out! Have changed diverter valve, has gone to fire boiler up, red light on and green light on but nothing happening at all. Thought he heard a "ping ping" noise every few seconds? Has checked all the connections everything seems Ok? please has anyone got any suggestions to try. Divertor valve just cost £130 to buy!! Many many thanks