"Christian McArdle" wrote in message
t...
This my third go at getting somewhere with my ailing boiler.
The problem now appears to be that the thermocouple is failing at high
temperatures.

If your boiler is old enough to take a thermocouple, you might want to
consider replacing it. A modern boiler would have 90%+ efficiency, instead
of the 50-65% you are likely to be getting now.

Can you explain how you calculate efficiency - is it for example :
Given the amount of heat ( in say joules ) that is released by the burning a
specific quantity
of gas, find the amount of heat transfered to the water and take the
quotient ?

Steve