Heater issues on 2008 X5 4.8i, 125k miles!

Could most commonly be one of two things (or both) 1-low freon level (even very small loss will cause a imbalance to multi zone bmw HVAC, and yes it will affect both heat and cooling, causing heat instead of cooling on one side of car or vice versa), add freon and see if problem solved. 2-replace water valve 64116910544 on your 08 bmw. Its is a common failure part and will cause similar problems. by default if valve is replace you should always check freon level. Its located between drivers side valve cover and fender/steering shaft. Has two solenoids on top of it and its inline to the heater hoses coming out of dash. normally, these cars need a small freon top off yearly to keep 4 zone hvac balanced out and blowing correct temperature air. It is often most commonly noticed at beginning of fall/winter when system pressures naturally drop, seals become hard and leak a bit, and when you call for heat it will blow out A/C. Quite annoying in 10 degree weather. normally just add freon. obviously, if no airflow is present or fan blower noise then check blower module/resistor and rarely the blower motor itself. also, regularly use compressed air (lightly!) to clean off internal car temp sensors or other erratic symptoms will develop. one is directly by radio volume knob on dash and has vent slits for access. another is on rear hvac also look for the vent slits. blow lightly to remove dust or may be damaged. there may be other sensors in the car however i do not remember their location. consult a bmw shop or shop manual. other more complicated issues may require a advanced (and very expensive) scanner or in some cases the dealer must use their scanner only.