I have the exact same problem with my CPA2. Went through the usual checks as above and even replaced the relay with a new one but the problem is still there. So now I think the only other component in the chain that can cause the problem is the IC that controls the motor etc.

Have not bothered going at it yet as I have been using a CPE2 for the past while until I build up the enthusiasm to order and replace the IC on the CPA2.

Be interesting to see how you get on.