Central Heating Question

I would say that there is a risk that the water in the expansion tank and pipes will freeze. As might any water associated with a cold water tank - if you have one.

My grandmother's house was empty for a couple of years before it was sold. I left the loft hatch open and the room stat on something like 12C, IIRC. Checked up on it every few weeks, and used a saucepan to ladle water from the cold water tank to the expansion tank occasionally (with the water turned off in the road).

When we did turn the water back on, the ballcock turned out to have been damaged by freezing at some point, and I had to replace it.

If we had known at the outset how long it was going to take to sell, I would have fully drained everything down, but we thought viewers would probably want to see a working heating system.

Also check what your insurance cover says. Cover for long periods away in the winter will usually require a full drain down, or heating running at something like 15C 24/7, or no cover for burst pipes and consequential damage.

That's what a £20 frost heater and a zero standing charge tariff is for.

Sometimes such systems have been fitted with no water feed. A single drop of mineral oil in the header tank should cut the little evaporation.

NT