Thanks Andy and flameport. I have a central heating electrician coming round tomorrow who is a mate of my brother in law who is a sparks.
The two blacks and two reds went to separate terminals ie there were 4 terminals and therefore they were not connected.
I have just replaced a very old room stat which had 2 red, 2 black and an earth. Drayton technical told me the wires to use from the old stat...
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