A Solar hot water anti front protection valve FPV can die of debris stuck in the seating seals or
What does 15mm, 1/2", DN15 or BSP mean? Why the thread diameter I measured won't match any of the advertised plumbing thread size? Australian BSP (British Standard Pitch) thread sizes for plumbing valves and fittings are only nominal and not the physical measurement for the thread diameter. This article explains BSP vs the physical actual thread measurements.