What is the snow flake mark on control for

AMANDA, January 2010

frost setting on rad valves or winter mode on boilers (heating and hot water on)

Ian, January 2010

think you talking about looks like this (*) this is called the frost setting this is the lowest setting possible,this prevents the boiler or rads from freezing up in very cold temperatures.the boiler will have one mounted separately in a cold garage, your TRV valves also have this setting on each of them

wirecutterman, January 2010

frost protection setting, i.e. a radiator valve with this on will only operate at very low temperatures

boiler bill, January 2010