However, the ASHP can also be used to cool your home in the summer. In the past this has been a dubious benefit for most of northern Europe, but heat waves have been getting stronger, last longer, and happen more frequently as time goes on. This is turning into a serious consideration.
Also, you can theoretically power a ASHP with renewable energy, while there are few if any carbon neutral replacements for natural gas.
Most boilers purchased today allow use with a Hydrogen mix, and some under development allow 100% hydrogen. Before the widespread extraction of natural gas, towns were powered with 'town gas', which is ~50% Hydrogen, so this is very much proven tech.
There are a bunch of potential ways to make green hydrogen too.
So, there very much is a path to green with a gas boiler.
Green Hydrogen has not worked out so far. It is not clear that it even has a path forward. There are a lot of people hopeful that it will be a solution in the future, but as of today it is so uneconomical that even people willing to spend more to be green don't use it.
But making green hydrogen has pretty bad efficiency. It could never compete with a heat pump using the same electricity source, even if it had an efficiency of 100%, since the heat pump has an efficiency of 200-400%.
Yeah, these can make ASHP a good idea anyway, but the grandparent was nevertheless correct saying that they don’t beat gas for heat in terms of cost in normal (I.e. not current) circumstances.
Also, you can theoretically power a ASHP with renewable energy, while there are few if any carbon neutral replacements for natural gas.