Keith,
can you tell if it is spinning by looking through the plastic cap. If it is spinning, then the check valve is mostly likely stuck closed. You can disassemble the check valve and free it up. I had one stuck closed on my 07’ Marquis, after freeing it up I have not had a problem since. I also checked into rebuilding the pump but was unable to get parts from the pump manufacturer. Was told Aqua Hot owned patent on pump and would not sell me any parts. Also, check your Ph of boiler fluid, if it is not correct check valves may stick closed. Hope this helps.