P11 occurs when the compressor discharge temperature (running parameter A1) exceeds 110C. 

Air Lock / Low Water Flow: Check for adequate water flow and remove any air locks in the system.  NOTE: If this this is a pool pump it will also be necessary to check/clean/replace the filter as required. 

Glycol Mixture too Viscous: If your mixture of Glycol is too rich, it will prevent adequate water flow within the system. Arctic Heat Pumps recommends a 25% - 40% mixture depending on your region and the mixture should never exceed 50%. If you believe this is the problem, replace the water with a leaner mixture. 

Low Pressure Sensor: Remove the jumper for Cn33 and check for continuity on the sensor line. 

If you do not get any continuity, place a jumper on Cn33 at the control board and try to run the unit. If the units runs normally you will need to replace this sensor. 

Expansion Valve: Check whether the main expansion valve of the refrigerant system is blocked.
Note: Specialized tools are required to test the expansion valves. 

manually open the expansion valve to the maximum opening to test whether the unit can run normally. If run normally then it's the expansion valve coil problem, if not, the valve damaged.

Refrigerant Leak: Remove the side panel off the Arctic Heat Pump and check for any signs of a refrigerant leak. Refrigerant is an oily substance and will usually pool at the bottom of the unit. You may have to check under the compressor and/or heat exchanger.

If a leak is confirmed you will have to call a professional to have it fixed and refilled. 

NOTE: It is also common for condensation to form inside the unit. If you find liquid and it is not "oily", it is likely condensation which is nothing to worry about.