> the boiler relies on an electric resistance in summer, when the house is mostly in equilibrium with the outside. That's the situation where a heat pump is mo

> the boiler relies on an electric resistance in summer, when the house is mostly in equilibrium with the outside. That's the situation where a heat pump is most efficient. I think you could reduce your hot water electricity cost by a factor of 3 by using heat-pumped hot water in the summer, instead of resistive heating. I guess the reason your system doesn't do that in summer is that it would require separate equipment. With the assumption of outdoor temperature 30°C and water 60°C, the theoretical limit is a factor of about 10. With so many people experiencing a cost-of-energy crisis at the moment in the UK, it's disappointing that these methods are rarely seen here. I've never seen a heat pump in a home in the UK.