On 20 Jan, 14:46, cynic wrote:

Never come across cast iron firebacks then?

Yes. They're bedded in mortar, which has a similar heatsinking effect.
If they're not, they can crack too.

Besides which, firebacks are cast in thicker sections than back
boilers.

Its probably not cast iron anyway but mild steel.

No, mild steel rusts through too quickly.


There's advice linked from the HSE site on a recommended process for
decomissioning. I think this was linked from here recently too. Mostly
(AFAIR) it involved a drilled hole moderately high up, then slowly
pouring dried sand down a pipe.