New RTS1 not sensing temperature

[Not-Ideal]

It replaces a much older RTS1

Heating comes on via timer or manual request even if dial is set at 10. Dial does click but always at same place ( about 25 )

It was replaced as heating was not coming on. Had insurance emergency visit , he said it was the thermostat and disconnected it ( some mention of link wire ). So at least we had heating.

We noticed thermostat was sort of hanging loose on wall ( not pushed in ) so bought and fitted a new one. However it is not sensing temperature.

I have attached picture of wiring which we did not touch.

 

[RandomGrinch]

Remove the grey wire.

 

[Mister Banks]

As above, the link from L to 3 should be removed.

 

[Not-Ideal]

That worked. Thanks