Bit of a strange one this ….. The heating system on Mrs Engineer’s ’07 Mini Cooper is playing silly buggers. It blows hot and cold for no reason and the air distribution and fan speed change of their own accord. I’ve looked on various forums and it appears that the cooling system is susceptible to airlocks. I can see why that would cause variable heat, but fan speed? I’ve tried to bleed the system, but it didn’t seem to have any effect. Any ideas? Ghost in the machine?

Sounds like a dodgy sensor to me.

which sensor?

Im guessing its got climate control? Probably the internal temp sensor giving iffy readings.

Or external temp sensor..

Bleeding the system would include having it on a run with temp set at max so that the valves that control the flow to the heater matrix open fully and flush through air in the system.

On that line, not sure abut the mini but bmw setups have a electronic valve that controls how much coolant gets sent to the heater matrix. Is normally located on the inner owing. It’s possible for the wires and connection block to dry up a bit and loose the electrical join due to the proximity to the hot engine. A good waggle of the wires and connector can ensure a good voltage gets thro and helps the valve open.

Also internal temp sensor normally is a fan that draws air over the sensor in behind the control panel. The inlet vent can block up with dust and fluff. A good Hoover of the dash can suck that fluff out.