Zanussi ZKG5540 with narrow travel of gas hob regulation knob

I have a second hand Zanussi ZKG5540 with four gas hobs and two gas ovens. The flame of the hobs is adjusted by knobs and it's supposed to go from minimum to maximum over an angle wider than a quarter of full turn (let's say 100 degrees rotation). In reality the angle is much narrower, especially with the smallest hob: it goes from min to max in what must be less than a 20 degrees angle.
The minimum is still at one end of the rotation but the flame stays at its maximum for most of the travel of the knob.
I have been using the cooker for quite some time and it's always been this way but I'd like to know what could be the reason for this problem and whether the hobs could be adjusted to operate as expected.

Does anyone here have any experience with such an issue?

Is mine such a rare issue? Anyone ever experienced this?

Loguc said:

Anyone ever experienced this?

Click to expand...

They might, but there are several problems here - gas cookers are far less common than electric ones, gas repairs are not DIY, and discussion of gas repairs isn't permitted on this forum either.

OK, thanks.