When I got my car the heat would not work, I gently tapped the valve with a very small hammer and it started working again.

I have seen a post on a UK forum where someone rebuilt their W124 heater valve with new parts - but cannot remember now.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)