If you say your not losing water or oil, an easy way to check if they are mixing is to check on the dipstick for tiny water bubbles if thats all clear then apart from you chucking out water through the exhaust.
Anyway, if your defo not losing water then its not your HG and it wont be your water pump as this doesnt effect the heater. As deano (i think) said check the thermostat, where does your temp guage sit when driving along? If it runs at cold or not much above it when goin along but happily sits half way when sat in traffic then it could be this.
If not i think the heater matrix has given up the ghost, are both coolant pipes goin into the bulk head hot?? Or it could be the actual centre console is faulty.
But these are purely guesses! Has this been happening for long or has just started to happen?
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Tuesday, 18 January 2011