Why Does My Geothermal Loop Keep Leaking?
Short answer: Because somebody keeps topping it off instead of finding the joint that leaks. In 47 years I have had three leaks in the buried loop. Two I found, one I never did. The rest were above ground, at pumps, hoses, fittings, valves and ports, and at Hartzell’s Heat & Air I find those with a pressure test and a flashlight.
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How often is the buried geothermal loop really the leak, in Hartzell’s experience?
Almost never. Here it is in my own words: “Out of my forty seven years of doing this, I’ve only had three loop leaks. Two were underground that I was able to find. One that I wasn’t.” Leaks in the mechanical room, where a person can reach them, I find all the time. My records since 2017 say the same thing: 700+ geothermal jobs at Hartzell’s Heat & Air, not one loop field replaced, and on the loop side, the parts that do get replaced are loop pumps, pump o-rings and flow centers.
The question still shows up as a verdict: my loop is always leaking. I went out to a customer whose loop had been filled a hundred times. Okay, I’m exaggerating. But within a few minutes I could point at the leaks. Both field videos below are from jobs like that.
Where does Hartzell’s look for a geothermal leak first?
Above ground, in the mechanical room, at every joint that is held together by a gasket, an o-ring or threads. A modern closed loop is heat-fused polyethylene. ClimateMaster limits in-ground piping to fused polyethylene, and it says threaded plastic-to-metal fittings should be avoided due to their “potential to leak.” The joints up on the wall live with heat, cold and vibration every day. These are the ones I check:
| What I check | What I am looking for |
|---|---|
| Flow center and pump flanges | Gaskets and o-rings under constant pressure and vibration, weeping underneath where nobody looks. |
| Hose kits and o-rings | The flexible hoses from the flow center to the unit. Rubber ages, clamps relax, swivel ends go first. |
| Fittings and adapters | Every threaded and barbed transition between materials. |
| Valves and the fill port | Stem packing, and a fill port that was not closed all the way after the last top-off. |
| P/T ports | A pressure and temperature port that drips just enough to matter without making a puddle. |
| Unit connections | Where the loop meets the heat pump, including any service valve that was opened. |
Why doesn’t a geothermal loop leak leave a mark?
Because some leaks are too slow. When loop fluid escapes and dries, it usually leaves a chalky mineral crust, and finding the crust finds the leak. But a slow enough weep off a warm surface never builds one. In my words: “It just doesn’t leak enough for the minerals to show.” Pressure keeps dropping, nothing is visible, so the loop gets topped off again and the joint never gets touched. That is why I pressure test instead of guessing. ClimateMaster’s loop leak bulletin has the inside piping and the outside loop tested separately, so a leak on the wall is never blamed on the yard.
When is a geothermal loop leak really underground?
Two cases. The first is older loops. They used an older style of poly pipe and push-together fittings instead of fused joints, and the pipe expanding and contracting through the seasons cracked or broke those fittings. Even then, the fitting failed, not the pipe. The second is outside damage. One I found was a pond loop. We fixed it, and a beaver chewed into it twice. The homeowner finally trapped the beaver and relocated it. Otherwise, real poly leaks come down to homeowner or technician error: a loop that was never pumped up properly or never sealed properly.
Should I put stop-leak or sealer in my geothermal loop?
No. My rule, in my own words: “Don’t be putting seal or crap in it.” A sealer cannot tighten a weeping flange or a cracked fitting, and it does not stay at the leak. It circulates through the flow center, the pumps and the heat exchanger. ClimateMaster wants loop fluid filtered to 100 microns when a loop is flushed, and a sealer works against that.
“Out of my forty seven years of doing this, I’ve only had three loop leaks.”Dave Hartzell, Hartzell’s Heat & Air, Kingfisher
What does topping off a geothermal loop every season cost me?
More than the visit. Every refill changes the antifreeze mix, because what leaks out and what goes back in are rarely the same, and ClimateMaster wants freeze protection held to 15°F below the lowest expected loop temperature. ClimateMaster’s bulletin also lists a noisy pump as a sign of low pressure or air in the loop. ClimateMaster calls at least one extra top-off after a complete heating and cooling season normal. Topping off season after season usually means an unfound leak. The part that bothers me most is the homeowner who decides geothermal is unreliable and tells the neighbors, when the real defect was a gasket. That is why I tell people to insist on somebody who does geothermal, and why I keep my IGSHPA accreditation.
What does Hartzell’s charge to find a geothermal leak in Oklahoma?
Pressure test it, find it, fix it, not top it off and drive away. The geothermal diagnostic is $348 flat, weekday, night or weekend, and the same $348 for my maintenance plan members, with a written report and a quote before I leave. The repair gets quoted after I know what is wrong, because quoting it before I find it would be guessing. Geothermal is statewide Oklahoma for me, not just my daily service counties. I am a ClimateMaster GeoElite dealer with 4.8 stars and 300+ Google reviews.
What you can do, and what to leave alone
- Keep track of how often the loop gets topped off and who did it.
- Look for chalky crust or damp spots under the flow center and hoses, from a safe distance from wiring.
- Listen for a pump that runs loud.
Leave alone: valves, ports, hoses, adding fluid, and any stop-leak product.
Keep going: the pressure test that finds a loop leak before anybody digs, common geothermal system problems, geothermal repair, geothermal maintenance, closed loop vs open loop, horizontal vs vertical vs pond loop.
Field video: loop pressure and fill-kit context
Field video: geothermal leaking problem
Questions I get about leaking loops
Why does my geothermal loop keep losing pressure?
Nearly always a mechanical joint above ground, not the buried pipe: flow center gaskets, hose kit o-rings, threaded fittings, valve stems, P/T ports or the fill port. A slow weep can dry before it leaves a mineral mark, so it gets topped off instead of found.
Can a buried geothermal loop leak?
Yes, but rarely. In 47 years I have had three leaks in the buried loop. Modern loop pipe is heat fused into one piece. The exceptions are older loops with push-together fittings, which seasonal movement cracked, and outside damage, like a beaver chewing a pond loop.
How do you find a geothermal loop leak?
A pressure test first, with the inside piping and the outside loop tested separately, then every mechanical joint in the mechanical room checked by hand and by eye for mineral crust or dampness.
Should I use a stop-leak sealer in my geothermal loop?
No. A sealer cannot tighten a leaking joint, and it circulates through the pumps and the heat exchanger. Find the joint and fix it.
Is it normal to top off a geothermal loop?
ClimateMaster calls at least one extra top-off after a complete heating and cooling season normal. Topping off season after season usually means a leak nobody has found yet.
How much does it cost to find a geothermal loop leak in Kingfisher, Oklahoma?
My geothermal diagnostic is $348 flat, any hour, and the same for plan members, with a written report and a quote before I leave. The repair is quoted once I know what is wrong. Call 405-375-4822.
Sources
The quotes are my own words from August 2026. Test steps come from ClimateMaster’s bulletin and manual below. Job counts come from my service records since 2017, rounded down.