Just a note on this topic... this happened to my parents a few winters ago (up in Canada). The new digital thermostats that run on batteries, if the battery dies while you are gone, the furnace state stays the same, ie if it is off when the battery dies, it stays off forever. My parents would set to 10C and have a relative check the house a few times a week so they caught it before the house froze. They would also turn off the water but if you have no heat the standing water in the toilets and sink drains can still freeze. For this reason they now change the battery before they go and pour RV antifreeze in the toilets and drains just to be safe.
Just another note on this. My insurance agent told me a story about someone in a neighboring town. They had a million dollar house and left for Florida for a few months. A battery failure like I described caused the furnace to not come on during a Canadian winter of -10 to -20C. Once the pipes burst, the water flow was too great to freeze up completely, so it flooded the house and turned the entire main floor and basement into ice rinks with foot thick ice everywhere, even going down the front porch and driveway. This continued for over a month unchecked. The house was totaled and not covered by insurance as a common stipulation on Canadian insurance policies is you need to have someone check your house regularly and turn off your water when travelling.
