The P01 error occurs when there is a water flow problem between the Arctic Heat Pump and the buffer tank. 

Water Valves: There should be at least two valves and could be many more between the Arctic Heat Pump and the buffer tank. They all need to be in the open position. 

Most valves are in the open position when the lever is in line with the input/output. 

This valve is open

The valve shown below is closed

*** If you have a different style of valve, please refer to the documentation to assure the valve is in the open position. 

CIRCULATION PUMP: The circulation pump between the Arctic Heat Pump and the Buffer Tank must be 220v - 240v. If you have installed a 110v - 120v pump it will not provide enough flow for the system. Please check the voltage label on the side of the circulation pump to ensure you have installed a 220v - 240v pump. 

IS THE CIRCULATION PUMP WORKING? Although the circulation pump is very quiet, you should be able to notice when it is operating by sound and/or touch. When the controller with the Artic Heat Pump indicates the circulation pump is engaged (see image below) check to see if the pump is working. 

If the pump does not appear to work, electrical troubleshooting will be required to isolate the problem. 

CIRCULATION PUMP SPEED: Check the pump to see what speed it is set to operate on. In our test facility, we use a Grundfos UPS26-99FC set to the maximum speed. If we have provided the circulation pump with your order, this is probably the model we would have shipped (see image below). 

*** If you have provided your own circulation pump please refer to the documentation to see if the speed can be increased. 

AIR LOCK: If the valves are open, the circulation pump is correct, and everything appears to be working then you may have an air lock.