Advice identifying the "TEACH IN" button on CH ptogrammer

[mart]

My C heating programmer works ok for the hot water but currently not for the heating. Apparently I need to syncronise (pair it) with the room thermostat. Also called 'binding'.

The instruction sheet says that the pairing is done by pressing the "TEACH IN" button. I cannot identify this button, so I am stuck. Can anyone help.

The HC60NG is the programmer.

The HCW80 is the room thermostat.

 

[mart]

 

[Blobber]

When the stat is off the base the teach in or send button is on the back in the bottom corner where the batteries are