smoke detector not triggering electromagnetic catch

We have three dors with electromagnetic catches linked to our smoke detecto rs. Origially they were all made by Menvier. One failed druing the building works and the electrician replaced it with a DRW-M Wall Mounted 230v Door Retainer.
Recently the Menvier one on the top floor failed. I tried to find a Menvier one on-line but couldn't so I bought another DRM one. Installation seemed simple live, earth and neutral. The catch on the middle floor has only one set of wires going into it but the one I replaced had two sets (presumably the return loop).
I replaced the top floor one as wired previously with the two sets of wires going into the appropriate holes on the connector block.
The catch works fine and is released when the button is pressed. However, w hen I set off the smoke detectors the catch is not released. The wires seem to be firmly griiped by the connector block. Any suggestions - did I buy t he wrong catch?
many thanks
Jonathan
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