Internal bell not working after Ring 2 install

I've just installed a Ring 2 doorbell for my father in law. The battery was fully charged and the Ring doorbell is working fine. Unfortunately the mechanical internal chime is no longer ringing. Then I touch the 2 wires together, it works fine. As soon as I connect the wires to the Ring doorbell and press the button, the internal bell no longer chimes. When I installed the same doorbell at my own property I did not have this problem. Any advice would be gratefully received.