"Andy Hall" wrote in message
...
On 12 Jan 2004 11:23:48 -0800, (RJ) wrote:

Not "that" red thing - I know that!

The thing in top-left corner on the top of the cylinder. It has an
electrical connector to it and I can't work it out. Its on the end of
a T for the boiler in/return.

I was going to say it's an immersion heater. The make is right and
the shape of the top is like an immersion heater cover. However,
from enlarging one of the photos it appears that it says 240v 3A.
An immersion heater would normally be 13A or more. Also I wouldn't
expect it to be located as described.

Where does the other end of its lead go? To a terminal box along
with the lead from the cylinder thermostat?

If so, then it's possibly a flow switch, pressure switch or thermostat
or something like that.

This appears to be a high temperature boiler cut out. It is on the boilers
return from the coil. If the return is too high it means the boiler is
running away. The cylinder is up and over temp and the difference between
the flow and return is minimal. It could be because of a number of problems
all occurring at once, which means the cylinder will get and hotter and in
danger of exploding if the pressure relief does not open.

Some versions of unvented cylinders have a high-temperature relief valve.
If high temperatures occur, typically 90-95C, the valve physically open to
an overflow pipe.


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