I haven't bothered to use the flue extension for several years, I always forget. Never had a problem in that time.

My manual states in section 9.2 the following:

"When camping in winter, the Truma waste gas vent extension should be used to prevent snow from choking the waste gas vent"

oh well that's good to now, I'd never seen or heard of it till on a forum the other day & the main dealers i bought it off never gave me one with it at the time or mentioned it . Again I'd never had a problem with mine but i don't tend to have the caravan hot, just a few mins in the morning usually.

Did the flue extension make that much difference to the fire being blown out? At the time of starting this post I’d never had a problem till this weekend which was pretty windy. I’d spoken to the workshop Forman at our local eriba dealer & he mentioned being blown out from underneath the floor where the cut out is for the air pickup . I have just received my flue extension pipe tonight but will have to see what happens in the future

It's true that the extension is really to ensure adequate clearance in snow build up on the roof, but it has the benefit of lengthening the flue which my day release course back in 1965 when my first employer (the NCB) sent us to get an ONC qualification on heating and coal etc, told me improved drafting and efficiency.