The P06 error occurs when the R410 Refrigerant Pressure is too low. When the error occurs the pressure gauge on the side of the unit will exceed will not climb when running, or may even be sitting at 0. 

Fan Blade(s): Check to see that the fan blades on the unit are clean and free of debris and clean has necessary. The fan must be able to turn freely, and uniformly. If you see any fan blade damage, or if the fan is shaking erratically you may need to replace the fan blade. 

Air Lock: A very common cause of the P06 error is air in the hydronic system. Make sure you bleed the lines appropriately to assure their aren't any air locks. 

Faulty Readings Check for continuity across corresponding pressure switch. 

Disconnect Cn33 from the control board, and check for continuity on the sensor line.  

If you do not have any continuity on that sensor, the sensor may need to be replaced. Please contact "Arctic Heat Pumps".

Refrigerant Leak: If the pressure gauge reads 0 or if you have exhausted all other troubleshooting, 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 refrigerant leak is confirmed, have the leak fixed, vacuumize the system and fill with refrigerant according to the information on the technical label.

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.