On Mon, 27 Oct 2014 08:16:20 +0000, Tim+ wrote:

What's the system pressure like? When did you last top it up?

Oops, I was presupposing it was a sealed system.

You presupposed right. I should have mentioned that. Pressurised hot
water cylinder, with solar HW. Wet underfloor heating. Does the exact
same whatever is on or off out of the heating (three zones/timers) or
water.

Condensate drain appears to be all internal. There's plastic heads
towards a wall and the back of the kitchen units, presumably joining the
sink drain.