Doctor Drivel wrote:
"YAPH" wrote in message
...

Having the main thermostat and the safety cutout both fail to danger
is extremely unlikely and I'm sure the probability of any given
unvented installation being subjected to these conditions is very,
very remote. However as the number of unvented installations - and
installations that aren't safety checked periodically - increases,
so the probability of *some* of those installations failing to danger
increases. And the
*consequence* of such failure is Not Good (tm).

Those who vehemently defend unvented cylinders over near zero risk
DHW only vented heat banks,

But it's not zero is it? You can't ignore the deaths from vented cylinder
systems if you are trying to prove that one system is safer than another.

(Sorry, I'm using logic again. Unfair I know.)

Tim