This will sound strange but take the knob off and stuff bits of aluminium foil inside the sleeve that goes over the knob stem.
Bought a new Force10 last year and one by one the burners would not stay lighted. After several frustrating discussions some one at force 10 explained the tinfoil trick. Seems they had some bad knobs but won't admit it. How you get away with that on a premium priced product like Force 10 is amazing.
They had several explanations mostly involving magical think but refused to provide new knobs.
; much improved over the older Force 10's I have had but would probably not buy one again.