I guess this post doesn't really belong in Boilers & Hot Water Tanks so I'll offload it in this subforum.   The central heating system in our house is fired by an ageing Glowworm Flexicom 30HX (heat only) condensing boiler. It's probably on its last legs but while it still works I'm keen to squeeze every drop of life out of it. The main drawback with it is that there's only one flow temperature (set on the front panel display with a couple of pushbuttons) for both heating and HW, w