Your Watermill Shower Pump will only work properly if it has been installed correctly. Ask your installer to complete the following check list, ensuring it is INSTALLATION INSTRUCTIONS. FOR REGENERATIVE. MAINS SHOWER PUMP. Model: PR35D Medium pressure twin. PR50D Medium pressure twin. PR50S Medium pressure single. This regenerative shower pump from Watermill is ideal for replacing an older or broken model. Trouble shooted it as per instructions but no sucess.