P11 is a protection sensor that trips if the discharge temperature exceeds 221 F. (possibly 230 F on some models).
The chief reason for this P11 error is loss of refrigerant. The first clue is to ask for the commissioning report, because it helps to see the setup values.
If we can compare initial pressure/temp with current it can shorten the process. If the pressure at rest drops by half over a few days, there is a leak.
- The Fix is to repair the leak
Another reason can be the water tank temperature is set too high, meaning higher than 50 C or 121 F. Setting the temp lower is just a workaround.
A lesser reason can be too low a flow rate. When a Grundfos 15-58 was on low speed, the problem stopped when the speed was moved up to medium for a 7 kW.
- Ensure there is about 5 gpm per 7 kW capacity at the system head pressure, or velocity above 3 feet per second so the heat is pulled away.