I see the Professionals are admitting to their limitations, whereas others keep going... If it wasn't so serious it would almost be laughable.
From my limited experience with solid fuel, the system had to be designed as fail safe so 'component failure' was never a factor. You cannot rely on anything with a possibility of failure to control a heat source that in itself has very limited control. This business of dumping hot water into the drains, and replacing with cold worries me immensely. Firstly I hope the property isn't on a metered supply, and secondly, what happens in the event of mains supply failure? I was always under the impression a heat sink capable of dissipating any excess heat safely was required, often a large radiator.