In an earlier contribution to this discussion,
Matthew Humphreys wrote:



Thats the controller / wiring box I have. - I was about to post the
same link!

It appears that the connection I have to pin 7 is permantly live. I
will check it out in the morning to see if I have wired the tank stat
incorrectly.

Can someone remind me the function of the connections on the tank
stat?

Cheers,


Matthew

The cylinder thermostat is in the form of a change-over switch. Pin 1 is the
"common" connection and is fed from Pin 6 in the junction box which in turn
is fed from the "Hot water required" contact in the programmer. When the
temperature of the water in the cylinder is lower than the temperature set
on the stat, Pins 1 and 2 are connected - so that Pin 2 provides a live feed
to Pin 8 in the junction box (and hence to the boiler and pump).

When the water gets up to the set temperature, the thermostat switch changes
over - such that Pins 1 and 3 are now connected. Pin 3 provides a live feed
to Pin 7 on the junction box, and onwards to the mid-position valve
actuator. This is the "hot water demand satisfied" signal and is used (via
the microswitches in the mid-position valve actuator) to switch on the
boiler and pump in cases where central heating is required but hot water is
not.

HTH.
--
Cheers,
Set Square
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