FWIW
From a cost standpoint, Bills suggestion of throttling down the pump output is a lot better than the following:
Homeseer 2 (which can use the CM15A as a powerline interface) has "Wait" timer resolutions down to milli seconds. So an "event" (macro) would use one wait timer for 20 seconds to enable the pump and a second 6 hour timer would control the pump cycles.
However if you use the CM15A as your powerline interface I do not think Homeseer can control any of the RF receive (transceive) and transmit functions the CM15A is capable of. Although, if you do use any RF remotes or motion sensors you could use a TM751 to transceive.
Be forwarned; Homeseer creates sticker shock when compared to AHP. But it is far more powerful, and more stable, with ability to mix X10 and Z-Wave for migration to newer automation technology. They have a unrestricted 30 day trial period.
http://homeseer.com/index.html Appologies to X10 for using the forum to plug Homeseer, but from a cost standpoint, they have no worries.