Cylinder thermostat & circulation pump problem

selectamatic

Turf fired range with back boiler supplies heat for central heating and hot water.

Had to change the central heating circulation pump the other day and when all was put back together the circulation pump was running constantly when given power.

We assumed the thermostat on the hot water cylinder may be the issue as it was old so got a new one today. Now the circulation pump will come on if the thermostat is set at 50 or 60 and up but it turns off at 40 and below despite the cylinder being cold.



This is how it's wired.

Mains brown live joined with thermostat red live.
Mains neutral joined with pump neutral
Mains earth joined with pump earth.
And then pump brown live joined with thermostat grey wire.

At the thermostat the red wire is at terminal 1 and the grey wire is at terminal 2 with terminal 3 left blank.

According to the thermostat wiring instructions terminal 1 is for the common contact and terminal 2 opens the circuit when the temperature rises. Terminal 3 closes the circuit when the temperature rises.
It then says normally (heating plants) use terminals 1 and 2.

selectamatic

May have just got it sorted by running the thermostat grey wire to terminal 3 and the red to terminal 1.

Circulation pump comes on when the thermostat temp is turned down to cold water temp and goes off when its turned up.

I'll report back when the water is hot if the pump comes on as expected.