The certificate is for building regs, the gas safe register notifies your local authority after the installer tells them its been installed, the installer should have self certified it at the time and the certificate is issued a few days later. https://www.gassaferegister.co.uk/h...tes-records/building-regulations-certificate/ It's likely the indemnity insurance is in case your local authority decides to take action because it wasn't notified or the appliance wasn't certified at the time of install. The reason its only 20 quid is because the chances of that happening are remote and the chances are it was probably fine (e.g. just the certificate is missing/lost/just didn't get issued). Everything has a certificate at the end of the day, even windows. If your happy with it then that's all that matters, its buyer beware when it comes to houses at the end of the day.