What pump are you using and what controller are you using?
The reason why I ask is that there was someone once on here who was having calibration problems with a Spring controller. He had replaced his pump with a small backpack pump which draws very little current.
Spring and Varistream controllers were designed to control larger pumps such as the Shurflo ones many window cleaners use. A Shurflo pump will draw up to 8 amps at full wack where a smaller pump may only draw a couple of amps which is outside the working amp parameters of the controller.
All I can say regarding 40 meters of pole hose on your hose reel is that you won't get a good flow through that size hose over a 40 meter length.
When trouble shooting we were always taught to ask what changed before the issue appeared. If there wasn't a problem before and there is now, did you replace hose, pump, fittings, etc.
With regard to replacing the controller with a switch; yes provided your pump has a pressure switch. What will happen though is your pumps pressure switch will fail with wear and tear sometime in the future. You can add a 40 amp 12v headlamp relay to the pressure switch circuit and use the pumps pressure switch to activate power to the pump. That will save the pressure switch. But again, 40 meters of pole hose is a long way to push a flow of water through.