BMW E36 heater not heating: water valve
Why does my E36 heater blow cold air?
The most common cause is a stuck water valve, which controls the flow of hot coolant to the heater core. Other causes are air in the system, a coolant leak, a faulty potentiometer in the temperature control and a burnt circuit board behind the control.
Where is the E36 water valve and how is it serviced?
The valve is in the engine bay next to the bulkhead, near the brake booster. Remove the covers of the valve and check that the spindles move and the coils are intact. In that case cleaning and greasing the spindles may be enough. Squeeze the hoses shut before removal and bleed the system after reassembly.
When does the water valve need to be replaced?
The rubber parts inside the valve can swell and block it, and cleaning does not help then. The resistance wire can also break. In that case the valve is replaced. The E36 valves are physically different from those of the E34, so buy the part for the E36.
How can I rule out a faulty water valve?
Unplug the valve wire. The valve then opens and hot coolant reaches the core. If the heat returns, the fault is in the valve or its control. The valve clicking every few seconds is normal.