Virginia Geothermal compressor shuts off after a few seconds, bad pump?

3.0 ton GeoCool geothermal heat pump
product #: GCHP01036V-LF-A
system has been running fine for 3 years

problem:

• in Cool mode, compressor starts for a few seconds, then shuts off
• air filter is new
• I see some amps flowing to the external pump, but I don't detect any water flowing thru the ground loop
• pump seems to be vibrating slightly, but I think this is coming from the main unit through the pipes

conclusion:

• my best guess is that the 25 year-old pump (Grundfos UP 26-99F) is not working
• because there is no water flow, the compressor shuts down to avoid over-heating

question:

• what should I do next to confirm it's the pump?

Thank you.

 

You should check to see if there are any lights lit on the lockout board. This will point you in the right direction to diagnose. Green is High Ref Pressure. Amber is Low Ref Pressure. Red is Flow Switch Water. Yellow is Condensate Overflow.

If it is the water flow switch it may be the pump or the loop is air bound. High Ref Pressure is also a symptom of low water flow.

Install Manual
http://www.geocoolheatpumps.com/geocool-installation-guide.pdf

 

I think the lockout control board is described here-
http://www.miamiheatpumps.com/Diagnostic.pdf

 

Thank you @geoxne, the green power light is blinking, and the high pressure green light is on but not blinking.