I came across a old floor mounted combi, a Worcester Heatslave. It must be 1970's /80's. It has a boiler and cylinder inside. I never had the time to figure out how it worked. Is it a thermal store with DHW take-off coil inside, like the older IMI Powermaxes? I was told this was the very first combi model on the market. Does anyone know how these old combis operated?