I am going away for a few weeks in the winter and I am thinking of shutting off the water supply at home; in case the heating system fails, I don't need to worry about pipe burst. I am just wondering if that is hazardous for the water heater as it will have to keep boiling the water for the heat supply. Will the water tank end up with no water and cause a fire?

There is a lot of confusing things here. Lets assume a water tank heater and a conventional furnace.

Water in a water heater doesn't boil. It's always replaced with new water. If the temperature and pressure is exceeded the T&P valve opens and constantly spews water out the pipe and possibly into the room or french drain.

Turning off the water does nothing for pipe freezing. You must drain the system as well.

The furnace can fail too. One common failure is that the blower keeps running.

The water damage is worth preventing.

For short vacations (1 week+), the heater is always turned to pilot or off for electric and the heater is set to 50 degrees. One problem is your furniture can be damaged at low temperatures as well.

If I went on vacation for 3 weeks in the winter, the water system would probably be drained.

Excellent advise.

Excellent advise.

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