Tunze ATO not working

[daplatapus]

Make sure the wire connections are good coming from the pump.
I've also noticed on mine that sometimes if it gets air in it (if for some reason it runs dry or something) I need to give it a bit of a shake and bump to work out any air bubbles in it.
Can you hear anything at all coming from the pump?
If you have access to a volt meter, you can also check the terminals feeding the pump leads to make sure the pump is getting power.