Chaffoteaux Britony 2T water heater ignition and pilot light issue

Hi, In Feb 2019 through Rated People I had a repair on the following: Fitted the following parts (already purchased) for a Chaffoteaux Britony 2T water heater: Electrode with lead Water heater diaphragm Thermocouple The water heater is again causing issues where the pilot light keeps going out and I have to try the ignition 20/ 30 times to get it to stay lit. Sometimes I can also smell a little gas when it hasn't lit up. I guess that happens when it's trying to ignite the gas and fails many times. Possible fixes: Same replacement parts as before New ignition unit Dirty/ blocked injector or wrong injector Blocked pilot head Faulty pilot tube New case seal/ gasket after fitting Can somebody please advise? Many thanks, Darren