Limit thermostat hot water

[telnet]

Hi, On my boiler I have a Teddington TB8 on/off switch combined with a hot water limit thermostat (see picture). The male spade connector on the left of this picture is labelled COM and the on on the right it is "Break on Rise".

Please can someone help me understand how it works. Clearly the sensor is a thermocouple device. There appears to be a single heavy duty, uninsulated copper conductor returning to the back of the switch above the Break on Rise male spade. Is this really a copper conductor or are there smaller wires inside? In general, how does the device work. For example, what signal does it send to the system?

My problem is the water in the tank is exceptionally hot even on the lowest setting. Please can someone help me understand how it works. \

 

[flameport]

The copper 'conductor' is a thin tube. The tube and the larger piece on the end are filled with oil, when the temperature rises, the oil expands and the pressure acts on a mechanical switch inside the main unit.
There are no wires, thermocouples, signals or anything else.

 

[fixitflav]

Teddington TB8 on/off switch combined with a hot water limit thermostat

That's not a high limit thermostat, it's the control-stat. The high limit stat only trips if the control-stat fails and doesn't stop the firing (or maybe some other fault). It then needs a manual re-set to restart the boiler. Presumably that isn't happening? flameport has explained how the control-stat works.

My problem is the water in the tank is exceptionally hot even on the lowest setting.

The lowest setting on what, the boiler control-stat, or a thermostat on the hot water cylinder? How it it all works depends on the system details. With some more information we might be able to comment.

 

[ianmcd]

as already advised that is not a high limit stat it is a control stat