Try to isolate the line with the leak and use an external sump pump and no less than a five gallon container.
Allow the water to circulate through the line and monitor the water level drop in the container. This will allow you to determine the water loss.
If not too severe add the GEOLOOP LEAK SEAL to the container, after following mixing instructions, and allow the solution to re-circulate through the loop.
If and when the level holds, you know you have stopped the leak.
Continue to re-circulate for an additional 2-3 hours.
Clear the line with air and let it set for 48 hours.
You can then pressure test the line between 10-20 psi.
If the pressure holds re-add your water, add the heat and pressure up to 15-20 psi.
In most cases, this method will work 80-85% of the time.
You now should have a leak repair lasting for many years.
If this method is not effective in your circumstance, a manual repair would be required.