On 27/11/2010 11:27, Thomas wrote:

So, what is the best way to prevent this in future? Pipe is about 20mm but I
dont really want to install a larger bore due to the need for a larger hole
through the wall. I'm in two minds about insulation - there's very little to
lag on the outside, but will lagging on the inside help or hinder?

Can't see why either would hinder?

I'm thinking the problem is probably related to the overall length of
the pipe. I suspect the drop on it is relatively shallow; maybe even
has a dip in it where water could collect (not even anywhere near the
frozen bit?) The point is that in most boilers, the condensate exits
via a syphon arrangement rather like a urinal toilet flush; ie rather
than dribbling water out gradually and continuously, which would
certainly encourage freezing up, it collects in a reservoir which dumps
all the water every half-hour or so. However, if you have a long, very
shallow run on your pipework, and certainly if there's any chance of
water collecting along it's route, that will cancel out (either wholly
or in part) the benefit of the syphon arrangemnent.

Or maybe you don't have the syphon in your boiler?

I'd suggest lagging the entire length (if you can raise the temperature
of the water exiting the pipe outside it can only help) and if necessary
increasing the drop on the pipe *especially* where it goes through the
wall (which may necessitate drilling a new hole).

HTH
David