On the Buccaneer avoid messing about with the pressure switch. It is a Whale pump and may need to be calibrated at the rear of the water inlet into the caravan. Again this is a last resort if you are satisfied there are no leaks and the onboard tank under the bed is full. In the 7.8 years we had our Buccaneer we never found the need to calibrate the water pump. The pressure switch is located by the onboard tank.
Make sure that the tap to the onboard tank is closed off. Also make sure that the tap for the hot water cylinder is closed off otherwise the water will drain underneath the caravan and the pump will continue running.
On the Buccaneer if the water in the onboard tank runs out, the system automatically switches to the aquaroll or mains water. If the aquaroll runs dry, the water pump system will automatically switch off after a couple of minutes.
On you on mains water or using an aquaroll? If aquaroll the system needs to be switched to ext which then fills up the onboard tank. Same with mains.