E39 blowing cold air when vent set to hot. Help

I noticed a few days ago the my E39 520 did not blow hot air from the climate control vents when I set the tempature to 26Degrees and
turned the the vent control to hot.
This is a new occurrence so I know something's wrong, but don't know what. I can see the engine temperature gauge right in the middle position which is optimum, and the temp guage works as expected, from start up to a driving, but the vent only gives warm air at most if I set it to hot.
What I did notice though was that I don't hear that little change of flow that you hear when you move the vent control from blue to Red. Anyone who owns an E39 will know what I mean. When you rotate the vent know to the red from blue, you get that gap in which the air flow drops then comes back, like something just redirected the flow. I don't get that anymore. I know cos, even when I turned off my AC I didn't get that weird smell that comes for a few seconds. so something is up. I've used the fault code reader and it came back with no fault codes. Anyone know what it could be cos at the moment it seems ok, but I like to heed the warning signs from the car which isa 98 E39 520i 110Kmiles.
Any help will be appreciated. Thanks
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