[The Coastal Craftsman]

It depends on if he has a pressurized heating system or a open vented system. If he has a open vented system then yes water will have to be left on but if he has a pressurized system then the water can be turned off. Even open vented system dont require a lot of water and the header storage tank would normally hold enough water to keep the system running for months but water does evaporate in these system so the water being left on is really a must.

 

[The Coastal Craftsman]

Now thats a reasoned alternative. However the boiler does need make up but the pressure tank will supply make up for months if the pressure doesnt bleed off from leaks. The well pump doesnt need to stay energised for the boiler makeup to function off of the charge in the pressure tank. Boiler make up rarely requires a cup full of water, does it?

If the system has been plumbed in correctly then a pressurized system should have zero water leak but even if it does you need to open a charging valve to charge the system back upto at least 0.6bar to get the pump to kick back in and the system run. even if you left the well water on, the system would not charge it's self back to the recommended pressure.

 

[The Coastal Craftsman]

This boiler is fairly modern...I doubt it will ignite with low water in the system.

If the system has a pressure dial built inot it then it's a pressurized system and 99% of these systems will not run if pressure drops below 0.6bar. If they system loses that kind of pressure to drop below 0.6bar then the system need to have a pressure test done and the leak found.

 

[The Coastal Craftsman]

The system is equipped with an expansion tank and automatic make up.

I have never heard of a automatic make up but if it has expansion tank then it's a presurized system. The system when upto pressure should be disconnected from the main supply so that if the check valve decides not to work then the heating water wont get pushed back into the mains water line and contaminate the mains drinking water or if someone turns on the refil valve it wont keep filing up the system to what ever mains pressure you have and cause an explosion.

As an example you should have a isolation valve then a removable flexable hose then a check valve(Non return valve) so that when system is charged you can shut of the water supply and cap the valves after you remove the flexi.

But you can shut of the mains water with this type of system. Also most new boiler have a low limit stat so that when the temp drops below a certain tempreture the system will fire up and run no mater if the stat is turned off or not. This is so pipes dont freeze over winter.

 

[The Coastal Craftsman]

Mike is also correct that you can add a Inhibited Antifreeze. Make sure that it's not a normal anti freeze as some of these are not compatible with the new aluminum heat exchagers. They should protect you to about -5 to -6 or you can do a massive dose which will cover you to about -20.

 

[The Coastal Craftsman]

I heard turning off the heat for long periods of time in the winter in cold climates can damage a foundation.

This is just one of the issues when it come to leaving heat off the whole winter. I have seen foundations crack in half due to heat being applied to a cold floor that was left over winter. The home owner had underfloor heating and he returned for his winter vacation home and turned his heat upto max and the floor cracked all the way from the screed to the foundation. He was meant to turn it up very slowly to let the floor expand slowly but he didn't. It can also ruin floors and walls. The other problem is water left in the pipes. You may think that you cleared out the whole system but water over time will build in certain areas like drops and elbows and water will freeze and crack pipes. Your best letting the system run of the frost stat so that it keeps it above freezing and shut of the mains supply.