how do i fix?

It's likely you have an in line pressure switch which causes the pump to think a tap is on. I get the same.
The switch is white in line near the water inlet. 1st ensure enough water in barrel tank don't run pump dry or you'll be replacing that.
To see what one looks like www.whalepumps.com click on the top right hand picture and you enter a pdf file scroll down to middle of page 3 there is the switch.

1. Turn the knob on top of switch in clockwise direction to close switch down but this will cause the pump to run.
2. Turn on the cold tap in the sink
3. Go back to the pressure switch and turn knob anti-clockwise until it starts clicking the water should pulsate abit then run smooth.
4. Turn tap off and pump should cease to function. If not turn tap back on and turn the switch knob a little more. I assume you have a 'pump in action' light over the sink or somewhere visual obviously when out pump stops. Not necessary but a pain when you only know the pumps running by sound.
Test turn tap on then off see if it ceases keep adjusting slightly as required.

bob
January 2009

Proabably a faulty micro switch on one of the taps, try disconnecting one at a time, new switches are available from dealers..

scotjim
January 2009