"Andy Dingley" wrote in message
...
On 9 Feb, 14:04, "Doctor Drivel" wrote:

A HepVo trap near the end of the condensate
pipe run that stops -0C air running up the pipe,

That's the beastie

If exposed to freezing air any moisture on the trap membrane could freeze
and then another blockage. They are best in a position where they are
unlikely to freeze and fitted vertically.