Rod - if I understand your question - it sounds like you think the pump should run when water is running? That is sort of true. The water system is a "demand" system that works off the pressure in the tank. When a faucet is open, the pressure drops and the pumps kicks in to raise the pressure. It does so quickly, so if the running water is not enough to keep the pressure down, the pump will start and stop as needed. In your example I guess when you open all the faucets, the pressure drop is enough to keep the pump running.
Here is a thread with some additional info that might be helpful.
http://www.trailmanorowners.com/foru...h+water+system
hope this helps.
Alan