hyblox

My daughter has an Apollo Hydroheat system and has been told she needs to replace her hot water heater. The only thing that is wrong with the system is the motor on top of the hot water heater is running continuously. After reading this forum, I question this recommendation. I plan on checking out if the service people who have been out are versed in hydroheat systems. The hot water heater is not leaking, there is hot water and the house is still getting heat. Can anyone tell me what would cause the motor to be running? What should I be checking for? Thanks!