Hi all
We have a glow-worm space saver Mk11 Balanced Flue Boiler in the kitchen, which is used to heat the water and supply the radiators when heating is required. Upstairs in the 2nd bedroom there is a cold water tank and hot water tank with an electric emersion heater.(never used).Also a motorised Mid Position valve (V4073a). Today on returning home from work, the hot water has come on via the combi boiler(no heating on) but the radiators downstairs were all red hot, even though the timer was set to hot water only and the thermostat in the hallway was on minimum.
The Boiler setup is a Y PLAN according to this site, if this helps..