In total, 1.67 million units were sold in 2019, an increase of 1.8 per cent on 2018 figures. The number of homes with central heating is also increasing, with around 22 million homes in the UK now having gas central heating, compared to around 17 million homes, 20 years ago.

Stewart Clements, director of HHIC, said: “HHIC estimate that the number of old inefficient boilers still being used by UK households is approximately 4 million. Inefficient boilers cost consumers more and emit higher levels of carbon dioxide than modern condensing boilers.

“The upturn in the industry signals a swifter demise of the ‘zombie boiler’, but if we are to reduce carbon dioxide levels at the rate demanded by climate change and help deliver lower bills, then a longer-term plan is needed to get rid of old and inefficient ‘zombie boilers’, so called because they don’t die, they just keep chugging away.”