I'm sure AC can explain it better.
Often you see figures quoted like
"Switching to an air source Heat Pump can help reduce your household’s annual emissions by 1,404 Kg of CO2, on average."
But they rarely give the figures of the air source heat pump.
I did find something close where it says
"Air-source heat pumps produce 850kg of CO2 per year compared to gas boilers which produce 2,500 kg of CO2"
Heat pumps, like renewable technologies, require energy for their production and raw materials to build them. They all have an initial ‘cost’ to our environment in their material extraction from the ground and the energy they consume during the manufacturing process.
www.renewableenergyhub.co.uk
If you believe those figures then an average family sized house air source heat pump will still knock out 850kg's of co2 every year.
If the intention is net zero, then by the industries own figures, net zero is not, and never will be, achievable