Guild Wars 2

Hi all!
My problem is really simply
Im Engineer lvl 80 Pistol/shield
In my shield i have a Superior Sigil of Life but the staks of this sigil dont increase my healing power.
I have tried to change the rune on my pistol but dont work….
I need this for my build.

Please fix it! Thank you for the reading

Are you sure that your pistol has no kill-stacking sigil in it ? and the said stacks are from sigil of life and not another ?

I have only sigil of life in stacking on kill.
With 0 stack i have 1258 healing power. With 25 stack i have 1258 healing power. The healing skill/trait dont encrease the health healed.