my heater stopped working for 1 week so i purchaced new thermostat and fitted it within another 2 weeks.after fitting all was well, heater and demister all working well.for about 3 weeks or so then it started. when i stopped at traffic lights or was in a traffic jam the heater would go cold and would not heat up until i started to drive with revs around 2000 this went on for afew weeks going cold then heating up again.then it stopped heating up again and is now back to no heater again.the temp gauge indicates half way up on meterengine runs well and does not overheat.is there a possibility that the temp control knob is not selecting properly.would appreciate any sugestions .

bill burke