I installed a closed loop geothermal system last fall. The water level in the loop by looking in the flow center had absolutely no perceivable change in level all winter. Now that it is starting to warm up outside and the system is operating in cooling mode I have noticed the water level has dropped an inch or so in the flow center. I just happened to be in the same room as the flow center the other day and heard what sounded like air flowing through the lines. Sure enough I saw bubbles coming in the return line to the flow center. It seems odd to me that the fluid level would suddenly start dropping at the same time it starts warming up. Do you think I have a leak in my loop or is there some trapped air that is being purged as the loop temperature is increasing?

I had a geo closed loop with 5000' of tubing and had to repressurize it every year. I just added new city water. With that much tubing water/methanol will slowly leak out.

Sounds like you have a place for the air to collect and be discharged....should be good

Do you have a pressure gage?

"Do you think I have a leak in my loop or is there some trapped air that is being purged as the loop temperature is increasing?"

Sounds like a non-pressurized flow center. Sometimes there is air trapped in loop that didn't get removed when first flushed.

I wanted to follow up on this thread. It does appear that ChrisJ is correct. The water level continued to gradually drop for about a month. It has now stopped dropping and remained at a constant level. Something with the increased loop temperature must have allowed additional trapped air in the system to be purged.

What about the tubing getting bigger and smaller with the temp change....

Summer your field will be heated thus expand and lead to lower water level....the winter would be opposite.

How long is your loop. Mine always lost pressure slowly over the year with having 5000 feet but never really analyzed it seasonally. How long is your loop?