A lot of the time the issue is that the condensate pipe is just too narrow. If you can, swap the external pipe for a wider one.
Ours is 2 inches thick outside would you believe…
If it’s not in the kitchen that can be a challenge. Ours is in the airing cupboard, only way that’s getting to an internal drain is by taking up the tiled bathroom floor… in hindsight we should have gotten it redirected when we had the bathroom done but we just didn’t think of it at the time.Is there a reason that the condensate can't be directed into a drain inside the house?
This would seem to be a less frost-susceptible situation.