G'day Cas,
Mate the old beast in short when powered gets up to the desired psi but instead of cutting out it pisses out air from a valve under a small black wired electrics box, which also has the on/off switch on top. And air also teems out of a small 90 degree plastic elbow directly under mentioned box? This then sends the comp into not switching off, and continuously cycles. Hope you can help and are familiar with my description.

Cheers hope to hear from you soon.

Kim