I work for the countries leading boiler installers and all I’ll say is, make sure you go with Worcester. Do you have a combi? If so, I’d go with at least a 25i. If you also have a shower which works off the boiler I’d go with the 30i for better hot water pressure. Generally you won’t need a bigger boiler than that. If you have any other questions feel free to drop me a DM so you don’t get ripped off. ??