E34 heater problems - help required!

[The T Boy]

My E34 540 is always blowing hot air into the cabin. The cause is that the heater valves are always open, allowing hot water into the heater matrix. I don't think that the valves are stuck as I had the unit apart a few weeks ago and all was fine.

I know that the "off" position of the valves is open - i.e. if there is no power to the valve unit then the heater is on.

However, there is a 3 pin plug attaching to the valve assembly and I assume one is an earth and the others should have power or not depending on whether hot or cold is selected on the heater control. On mine I always get power from the middle pin and nothing from the other two irrespective of whether the dial is set to hot or cold. Is this how it should work (meaning my valves are just stuck) or have I got an electical problem?

[Mroad]

I would say it would be unusual for both valves to be stuck, try tapping the top of the valves and see if it makes any difference.
I had a similar problem with my M5 except one side would blow hot all the time and the other side would be OK. I thought it was a stuck valve but it was also blowing from incorrect ducts to what was set so tried swapping the heater control panel over (the wheeled variety) which sorted everything. Try checking the panels connections at the back (unplug and replug) and replace if no joy, used spares can be had from Ebay for about £15-£20, cheaper than the valve.