ive had a think about it and if my pump was failing my car would overheat.if my matrix was blocked slightly it would explain why the heaters get cooler when you leave them on cos whatever shit amount of coolant that its carrying due to poor flow would be cooled by the fan inside the car,also explaining why they go warm if you turn the heaters off for a while then back on which is allowing time for more hot coolant to enter the matrix.what do u reckon does it make sense