Location?...you plan to shut off the boiler?

IMO

It may get to -15C. I don't intend to heat the house if it's unattended for the winter.

I would get your boiler service dealer involved for his recommendations and let him perform the work.

IMO

Thanks. Any general recommendations about what to be aware of or concerns?

You might want to consider leaving the heat on Low for the winter. One burst pipe and you'll never leave it off again! Also, even if you leave the heat on Low, turn off the potable water and drain the pipes when you leave.

Radiator water has no place to expand, so it would have to be drained or it would freeze and break pipes or fittings. I have read that some systems can use antifreeze, but I've never seen it used. All water supply pipes would also have to be drained to prevent freezing. You can usually add approved antifreeze to P-traps and toilets to keep them from freezing.

Also, over time all the oxygen leaves the water in a radiator system so it then causes very little rust formation in the iron pipes. However, if you drain the pipes you will expose them to oxygen in the air, and then again to oxygen in the fresh water you add. That may cause issues when you restart the system because there could be quite a bit of rust.

Bottom line- you need to leave the heat on and keep the house at about 50-55 degrees. This temperature usually ensures that water is unlikely to freeze, unless you have some fixtures that are more exposed to the cold (hose bibs, etc.).

Bruce