Turn water off but leave heating on during holidays with UNVENTED system

[SuperCow73]

Hi there

Per topic, is it OK to have heating on (to avoid freezing pipes) but turn water off (to prevent catastrophic water damage) during holidays with an UNVENTED system? I saw previous answers that it's OK to do so with a traditional system (i.e. water tank in the loft), but could never find an answer for an unvented system (Megaflow equivalent). As I understand it an unvented system takes its water from the mains (not a closed system) so cutting off the water could cause a problem in case it needs topping up?
I would appreciate any advice on this!

 

[flameport]

It's not a problem.
The hot water cylinder will remain full of water - with the supply off, you just won't get any hot water out of the taps.

so cutting off the water could cause a problem in case it needs topping up?

Unvented cylinders don't need 'topping up'. If a hot tap is turned on, cold water enters the cylinder and pushes the hot water out. It's completely full of water all the time.

The sealed heating circuit would need water adding if there was a leak, but that is a manual process anyway, so with no one there it won't make any difference either. The absolute worst is that if the heating circuit did leak, the pressure will fall and the boiler will stop working.