I suspect that the graph is for a NEW system. IE a blank install, not a replacement gas boiler vs a new install heat pump.
At which point the marginally cheaper boiler shows on the graph as such.
What is interesting to me, is that the cost of the initial gas boiler to run is lower than the heat pump each year. When the boiler is replaced (at a seemingly sensible cost, which also supports my first line), the ongoing costs of the second boiler are clearly higher.
Maybe this reflects some known thing that will happen later that will make them more expensive to run, higher regulations or something similar.
Almost certainly those lines will include annual maintenance etc (which heat pumps should have) but in reality the values on that graph are high as most of the cost of both will be running rather than install over that type of timeframe so other costs will be low and wont show up.
Plus probably more importantly they will have been averaged in, so eg the annual services, maybe some gas top up for the heatpump system around year 4, 8 etc. You wouldnt put then at exact timeframes unless they were hard coded in and could affect your when to replace decision.
You would average the maintenance costs across the term to show the relative values over time.
Which is why I think most people will end up with air to air heat pumps (aka air conditioning) and potentially a few electric rads in seldom used rooms where it doesn’t make much financial sense to put in heat pumps. I just don’t know why more people don’t talk about that solution.
Much cheaper to install, slightly more efficient when heating, can cool, very responsive like a gas system and they can now also heat hot water cylinders on the same multi split.
The downsides are obvious, installations can be ugly and internal units have a fan (noise and you don’t want to place them somewhere where they will blow on you as they take away the thin bubble of body heated air away from you).
Sort out planning and this by far a more likely end game for many.
Depending on the property either a smallish heat pump main system to do the water and some background heating via an already installed water system, plus some AC type units in high usage / high temp required areas and then many options for irregularly used rooms if they need to be up to temp.
Such as the heated wall paper idea, local elec heaters, boost the local rad via an element (isolate and heat directly like an electric towel rail) etc etc
