Indirect Water Heater

No, there isn't -- for the simple reason that it has no power to begin with. The indirect water heater gets the heat for the water from the boiler (it's a boiler, not a furnace, by the way). When the hot water gets cool, the switch -- called an aquastat -- on the water heater turns on the boiler and the circulating pump, and the boiler heats water which then heats the water in the tank (there is a coil in the tank, so the boiler water and your drinking water never mix).

Now you do have a different consideration: turning off the water in a cold region house. Should you? Perhaps -- but the hot water heat might need water from time to time if there is a small leak in it, and if all the water in the house is turned off and it needs water, it won't be able to run. On the other hand, draining all the water including the heating system is very difficult -- and, if it cold and you want to restart, almost impossible to do.

Some heating systems have antifreeze in the water. Do you know if yours does? If it does, it may make sense to turn off and drain the domestic water when the house is left empty. If the boiler fails, you won't be faced with frozen pipes. When you want to restart the house, just bring it up to temperature and turn the water on and you should be good to go.

If you don't have antifreeze, or if there is an automatic fill (pressure maintaining valve) connected to the domestic water, I wouldn't turn it off or drain things. What I would do is maintain the house at about 45 to 50 with the boiler, and either have someone reliable check the house every day or have a temperature alarm which will notify you if the heat goes off -- and have a reliable person on retainer who will get over to the house at Oh Dark Hundred in a blizzard and take steps to either drain the house or restore heat.

In this instance I’d put a WiFi thermostat to monitor the heat so in the event the burner fails, you can get someone there before a freeze up.
Modern oil burner primaries have dry alarm contacts that can trigger a call as soon as the burner locks out.
I would leave the water off when vacant and protect the boiler with a LWCO.
In the event of a power failure, runout of oil or some other catastrophe that causes a burst pipe/freeze up, at least the house won’t be destroyed by water damage.
If you keep the WIFI on year around, I’d put in some blink cameras to monitor too. Also there are WiFi tank monitors to help prevent a run out.

If I were doing it, I'd shut off the main water -- but I wouldn't drain the system down. Then the tank would still have water in it. However, if you did drain the system down it shouldn't hurt the tank.

And I will repeat: a Wi-fi alarm is a wonderful thing. It will tell you -- unless the power goes out -- that you have a problem. Some may even have enough battery capability, coupled with an on-site or on-board cell' 'phone capability, to let you know that the power is out.

What they won't do is fix the problem or take any steps to minimise damage. If the property is to be unoccupied frequently, particularly for more than a few days at a time, I still recommend either having someone swing by and keep eyes on daily, or have someone on retainer who can be notified when there is a problem and do something about it.