Canon Gas Cooker Harvest 10 year old?

My mother is 92 years old sge she has had a Canon Cooker for approx 10 years. It looks as good as new.
the taps for turning on the oven and Grill had broken and she had some replacements but they haven't got the numbers on them only the flame sign and it is difficult to tell how high the gas has been turned up. the oven does not seem to get very hot.
Please would you advise.