"always use with a check-valve"

[WaterTight]

Flexible Hose 15mmx15mmx10mm bore 300mm - NoLinkingToThis, Where the Trade Buys

Why?

 

[Plumbstar Tom]

its just to cover them selves as they don't know where your going to fit it

 

[Centralheatking]

Flexible hoses used to be for connecting equipment to the fixed copper pipe system.

The unit whatever it might be could be removable/temporary or of dubious performance

So as Plumbstar t above writes its their way of covering the application.

centralheatking

 

[ferret]

maybe because they are cheap they expect them to split open at some time ,and think a check valve will stop a flood , ha ha