JonG wrote:

Given the current weather, anyone any ideas what causes problems with
condensing boilers when it isn't the condensate pipe? CAn flue pipes
themselves freeze?

I have a 3-month old Worcester Greenstar CDi COnventional,

....
Everything has apparently been fine til today, we had hot water and
radiators the morning. May or may not be relevant that this is the first
day for a fortnight where daytime temperatures here have struggled to
marginally above freezing.

....

Outside, the flue did not appear to be frozen - there were some water
drops on the lower pipe, and it all sounded perfectly hollow. To be
sure, I poured a large jug of fairly hot water over it, back inside,
more water then appeared inside the boiler apparently from somewhere
around the flue exit, so presumably either from what I had poured on or
possibly from something melting internally.

Further thought is that the water I poured over it was finding its way
in via the inlet part of the balanced flue, which would suggest that the
initial water was mel****er and the warmer (or, at least, less extreme)
temperature Is relevant.

--
JonG
.... the hydrostatic paradox of controversy. Don't you know what that
means? Well, I will tell you. You know that, if you had a bent tube,
one arm of which was of the size of a pipe-stem, and the other big
enough to hold the ocean, water would stand at the same height in
one as in the other. Controversy equalizes fools and wise men in
the same way. And the fools know it. Oliver Wendell Holmes