Make sure no tap is left dripping. If that is not possible put a plug in the basin or bath overnight. Drips cause ice to block waste pipes. Never allow cisterns to over-fill. Water in overflow pipes can freeze, causing the cistern to spill at the sides. In a long cold spell, open the attic door occasionally to let in warmth from the house. During cold periods if you have to leave the house for short periods, keep the central heating turned on, turned down to the minimum. For long periods, drain the plimbing system by closing the main stopcock and opening all the taps.