Stuart turner monsoon 3.0bar negative head pump

[jamesBen80]

I've got a fault with a Stuart Turner 3.0 bar negative head pump. The other day it just didn't come on when you open the shower valve. I phoned the manufacturer and they no longer sell services kits so it's £550 for a new pump. I decided to remove it and give it a good clean, non return valves, flow switches and pump impellers. All looked fine and free, put it all back together, still won't come on, so I used a strong magnet to test the flow switches and still no change. I removed each flow switch and put it across a multi-meter and checked the resistance with and without the magnet and they close and open when a magnet is moved past them, so all seems ok. I then decided to rule out the motor and connected it directly to the live and neutral (disconnecting the circuit board so I don't damage anything) and it sprang into life and works fine, so I now know the motor is fine. Must be a control issue. Found a replacement pressure switch online, fitted it still nothing. So i decided it must be something on the little circuit board, a genuine one was £117+ vat, so I found an aftermarket universal one with good reviews online, fitted it tonight and now the damn thing comes on but won't switch off! I'm feed up of companies not supporting products after only a few years forcing you to buy new, Stuart Turner pumps are top end and should sell spare parts for a number of years. Anyway can anyone offer any suggestions, could it be the non return valves on the inlet letting by, or maybe a fault with the expansion vessel, I was told if you have issues with the pump starting and stopping to increase the pressure from 0.9 to 1 bar, i have tried this buts it very hard and the pressure always drop a fair bit when i disconnect the pump from the valve so its hard to get an accurate setting. Any other ideas before i fork out for a new pump?