If PS is displayed, this means that the pump's pressure switch has been operated due to a high build up of pressure in your system. The controller is set to work with a 5.2 litre per minute pump up to 100psi, although it will work at higher ranges. Common causes for the pressure switch operating are:
1. A restriction to the water flow, i.e. from a twisted hose.
2. Blocked or small water jets. (We recommended that the jets are no smaller than 2mm).
3. Grit or dirt trapped in the system.
4. Air trapped in the system.
5. Prolonged shut off of the water flow.
It is also worth just checking the above as something is causing a higher pressure build up than normal in your system. Have you changed any fittings recently? In which case you will need to reset the calibration using the auto cal.
Let me know how you get on