The now-ended Renewable Heat Incentive (RHI) was an incentive scheme that paid you a tariff depending on how much heat is used. It finish early in 2022.
The RHI was substituted by the Boiler Replacement Scheme in Spring 2022. The Scheme is grant of £5,000 for Air source (ASHPs) or £6,000 for Ground source (GSHPs), and is payed via an MCS installer.. It is effectively a discount on the installation bill.