Heating problem

Long story. I got my fabia 1.4 2001 classic from a non Skoda dealer and have had several problems but the latest seems to be a rather akward problem. A week ago the heating just would not work was taken back (still under warranty) to Rayrigg who took the car to skoda to have the heating sensor replaced.some 140 miles away. heating worked for 2 days, then temp gague went mad up and down from middle and heating stopped working. Took back to Rayigg who took the car to Windermere to be repaired

Ok car back heating working but temperature gague not; again bobs up and down as it pleases they have asked for the car back on 21st to have the temp gague and thermostat replaced. Is this normal for a car this age and is it a common problem.