How can I check boiler safety?

The problem seems to be due to the thermostat failure of immersion heaters....the water in the copper cylinder boils, and steam goes up the expansion pipe and exhausts into the loft header tank - which it is supposed to do. However the plastic tank can't deal with this high temperature and it splits, causing hot water to pour through the ceiling. However, if the water is boiling in the copper cylinder there would be considerable noise as the steam bubbles up the expansion pipe - the major clue of trouble. The cold water tank above would also contain very hot water, so any hot water coming from gravity fed cold taps would also indicate trouble. Any thermostat can give trouble though, so listening to the boiler itself will give the indication.

John
January 2008