Over the past few days with the cooler weather it seems that I've uncovered an issue that didn't really present itself during the mild spell but is now apparent. The issue is as follows; The engine reaches normal temperature after around 5 or 6 minutes (as per usual) but the heater air is only slightly warm. I first noticed this when I purchased the car a few months ago and at the time I mentioned it to the seller. He revved the car to around 2,000 rpm for about 30 seconds and then the heater was nice and warm and on my drive along the motorway it was nice and toasty inside. What I have been finding this week whilst sitting in a lot of stop start traffic and just idling for long periods is that the heater air is cool - not cold, but far from being warm. the length of time I'm driving for doesn't seem to make any difference but what does seem to get the heater working is when I hit a nice clear stretch of motorway and the revs increase over a sustained period of time. Any thoughts on what this could be? I had read somewhere about water pumps on these. there are no other symptoms. Thanks in advance.