Input monitoring while playing the recorded track

I have enabled input monitoring on the channel I'm using for vocals. The singer wants to hear some reverb (and is OK with the latency). On headphones we can hear the reverb when the track is stopped and when we are actually recording onto the track but cannot hear any reverb if I press 'play' without recording (i.e. when practising). I've tried using the reverb as an audio effect on the channel, as a send (using a bus) and I've tried sending the whole signal via a bus. None of these seem to make any difference. Can anyone help?