Even a well-insulated house with plumbing built to current codes can experience a disastrous water leak from frozen and burst pipes. But this problem usually only happens when the heating systems fails during cold weather and nobody is home to notice. The classic example is a house left empty while the owners take a winter vacation. There are several things that can go wrong:
The furnace can malfunction and fail to start. Some old furnaces use a standing pilot (a small flame that stays lit) which can be blown out by strong winds sucking air up the chimney. But there are lots of reasons why any furnace can malfunction.
The power can go out for a long period.
The fuel supply gets shut off. If the fuel is natural gas, there is a very small chance of the gas supply being interrupted, as long as the bill gets paid. If the furnace had a standing pilot and the gas was shut off for just a few minutes, the pilot will go out and stay out.
The fuel supply runs out. This is possible if the house is heated with propane or fuel oil and the homeowners go away, not realizing that the fuel tank is approaching empty. What if the owners go away for a short trip but are unable to return before the fuel runs out? If their fuel supplier regularly fills the tank (i.e. without needing to be called) this problem is avoided. But some people, for whatever reasons, aren’t on the “automatic fill-up” plan. Those people need to be aware of the risk of running out of fuel if they go away during the winter.