My plumber removed the antifreeze from my boiler and replaced with water which is fed from my well because of corrosion. I am leaving for the winter and would like to shut the power to the well and my plumber doesn't recommend it. I have a shut-off from the main water line to the boiler. What is the worst that could happen if I shut the well down? I will be gone for 4 months an feel uneasy leaving the well on. The heat upstairs will be set at 50 and in the basement at 50 as well.

You need to blow all the water out of your system with air pump or you may get freezing pipes and things like that which will crack. When you get back you will have to prime the pump which is no problem if it is plumbed right to do so. Also you will have to spend time getting the air out of the system. Start from the highest point in the system and be ready to do this a lot until it stops vapor locking. You can get flood insurance for replacement value and not worry about it and leave it on.