Return pump priming needed?

[intarsiabox]

If the check valve is closed when there is water in the return lines and the pump is off then it is doing its job. If it was open it would syphon water out of your tank and into your sump. However this doesn't mean that it is not faulty. It could be binding internally or spring pressure to great for your pump (assuming it is spring return and not a flapper valve). Can you put a spacer piece in place of your check valve to make sure that the CV is the problem? Is there a fitting between the pump and check valve that you could loosen to release any airlock?