Shuttle - Hooooston we have a problem - beeeep

Recently we thought we were a little nuttier than normal. Both of us were having hot flushes aka Tropical Moments. Then the penny dropped.
The heating was coming on every time the hot water was turning itself on. This is caused by a failure of what is known as the diverter valve. The bloody bit in the photo.
One engineer, one mug of tea and 20 minutes, fixed. Our service contract has just paid for itself. Fortunately our water is so soft the valve has lasted 12 years.

(Title - It's also known in hydraulic systems as a shuttle valve)