From what I have dealt with, and others I have read about, the problem is probably the monovalve and not the aux. pump if you have
no heat. There is a rebuild kit for the monovalve and takes all of 15 min. to repair.
The aux pump usually shows up as
weak heat especially at idle. (I believe Carrameow had a write up with pics on rebuild.) I don't think the motor is available separately though. An advanced search will turn up more.
Also, note that these are both controlled by the ACC controller. Bad solder joints in the controller can give you the same problem. (It is hard to believe that folks are complaining about no heat.
)