On Dec 21, 8:22*am, " wrote:
I'm about to go away for a few days, and usually I would switch the
central heating thermostat down to the frost setting.

That of course will be sufficient to ensure that the pipework inside
the house won't freeze, but my feed & expansion tank is in the loft -
and with the exceptionally cold weather, I could imagine that might
freeze.

My system is a thermal store (i.e. large volume of water), so hot/cold
cycling actually results in a fair bit of movement of the water level
in the f&e tank. I'm guessing that because it's never off for more
than 8 hours on the current timer settings, that any ice "skin" in the
tank gets broken up by the movements in water level.

So I think I'm going to play safe as temperatures are remaining below
freezing for days - and leave the system on its normal settings.

But I'd like to hear - are f&e tanks freezing a real problem?

Are burst pipes elsewhere in the system (due to inadvertently creating
a "sealed system") a possible outcome?

You can drain your hot water loft tank down by turning off your stop
tap and turning on your hot water taps. This drains the loft tank but
not the cylinder.
As the float valve is open, you can drain the coldwater pipe up there
by opening the cold taps about the house.
However you C Heating tank is at danger. I have seen the trick of
putting an extension lead with 100w lamp beneath the CH tank. I
imagine there's a small fire risk with this or the bulb could blow
leaving you without protection.
Maybe a small tubular heater? (Needs air circulation or may over heat.)