A U.K. couple with energy costs approaching £400 a month expected their failing gas boiler would be the next thing they'd replace. After looking closer, though, they realized they could install a heat pump for about the same upfront cost while also reducing their utility bills. What happened? Homeowners James and Kinga told Heat Geek (@HeatGeek) their century-old semi-detached house in Folkestone came with a heating setup that was hard to manag…