Sounds like you need to fine tune the pressure switch setting on the pump.Follow the instruction on this bottom section of this page:http://www.gardinerpolesystems.co.uk/acatalog/What_pressure_delivery_pump_will_I_need_.htmlSounds like the spring inside the pressure switch has slightly altered with age and needs to be adjusted so that it cuts off more positively. Follow the steps outlined on the web link and it should remedy the situation. Should take no more than 5 minutes with a Philips screwdriver!