1992 BMW 318 I (C) heater problem

Hi, I"m new, w/ a question re heater problem in a 1992 BMW. While driving last winter, heater went out and car overheated. If high rpm (acceleration or gearing down) heater would work and overheating would go away. Checked Thermostat; ok but replaced anyway. found water leak in front and top of engine; replaced water pump and head gasket. Heater still doesn't work unless accelerating, but car no longer overheats. Does anyone have a solution?

Galahad412