"Christian McArdle" wrote in message
et...
1. Vent pipe dipping into water in header - thus setting up a
thermo-syphon
system which heated up the header tank

I concur. Normal heating expansion shouldn't heat the cold cistern. This
needs to be fixed urgently, as (a) it isn't safe and (b) it must be
costing
a fortune keeping the barely insulated cold cistern at 60C using
electricity.

Christian.

P.S. I would always fit a dual thermostat immersion with a manual reset
trip
set 10C above the main operating thermostat. These are required for
unvented
cylinders, but heartily recommended for other types of cylinder too.



this is the first time it has been known to happen, though (heating the
storage tank). They say that the immersion was left switched on for a day,
I have suspicions that it was far, far longer than that, though...

--
Richard Sampson

email me at
richard at olifant d-ot co do-t uk