The lower the temperature you let your house drop to, the harder it will be to bring it back up, and correspondingly expensive. I would support advice regarding setting your thermostat to whatever temperature which you are prepared to accept as a minimum (I would suggest no less than 10). But I would leave all internal doors open so that the temperature throughout is even (otherwise you may have problens with such things as condensation at some stage) and (importantly) leave the heating on constantly and not timed - it will only be activated by the thermostat when necessary (there is no such thing as wasted or unnecessary heating, unless you want temperatures to drop uncontrollably). Unless your loft/attic normally relies on heat from the rest of the house there should be no need to deliberately vent heat into it (that would be wasteful). If you are unsure of the quality of the protection of any piping and tanks, then there are two ways to take action: one is to leave both hot and cold water running very slightly (into a sink or bath), the other (better) is to turn off the water supply and drain all pipes and tanks (except the expansion tank to the central heating).