On Friday, 6 January 2017 19:39:53 UTC, wrote:

Clarification - I should have made clear that the water hammer (when it occurs in a nearly-fully-heated cylinder) is not the few-Hz bang-bang-bang, but more more like more-or-less continuous-tone vibration noise that randomly rises and falls in loudness, randomly dropping to barely audible for a few seconds only to increase again, and continue until the boiler finally cuts out.