Sorry if i'm a bit late with this.
You need to recoat Rationel windows every year with the acrylic coating supplied from Rationel (They're in Edenderry if that's near to you).
The 2 to 3 years the sales person would have quoted is for scandanavia, the damp here attacks the timber, it's nice and dry that far north.
They're fiddly to paint, but the coating is easy to work with & water based. Windows and doors will look refreshed as theres a slight amount of pigment in the coating.
I think i paid about 40 euros for a half gallon & i used about one fifth for the outsides only, store the rest in the shed, shake well before re-using the following year.
Older Rationel windows used an oil based varnish, best check with Rationel what yours are.