On 03/03/2018 12:53, Roger Hayter wrote:


You spotted I put them in reverse order then! And I'd actually
forgotten that some people have them quite high up. It must have been a
small risk with pre-condenser flues, but I suppose that very little
condensed out in those days.


When we had a cold spell a few years ago (-17c here) several of the
neighbours flues froze over with the condensate. They were all
conventional boilers and they had to go out and chip the ice away. It
could have been really dangerous if CO had got into the houses.

My balanced flu, non condensing boiler didn't ice up.