Why Does My Geothermal Loop Keep Leaking?
Three. In forty seven years I have had exactly three loops where the buried pipe itself was the leak. Leaks in the mechanical room, where a person can reach them, I find all the time. That gap is the whole answer.
4.8 stars, 300+ Google reviews
This is the most common geothermal question I get, and it arrives as a verdict: my loop is always leaking. I went out to a customer who had been having his loop topped off for years, a hundred times the way he tells it. Within minutes I could point at the leaks.
Buried pipe almost never leaks. Fittings and pumps leak constantly. If somebody has been adding fluid for years, nobody has looked in the right place yet.
Why the buried pipe is the last thing I suspect
A modern closed loop is high density polyethylene and the joints are heat fused: the pipe ends are melted and pressed into one continuous piece, no seam and no gasket. Buried, it will outlive the house on top of it.
Above ground is the opposite. Every mechanical joint lives in that mechanical room, held together by pressure against a seal, and seals take heat, cold, vibration and years. That is the part that gives up, and the part I can reach.
Where I actually look, in order
| What I check | What I am looking for |
|---|---|
| Flow center and pump flanges | Most common by far. Gaskets and o-rings under constant pressure and vibration, weeping underneath where nobody looks. |
| O-rings and hose kits | The flexible hoses tying the flow center to the unit. Rubber ages, clamps relax, swivel ends go first. |
| Fittings and adapters | Every threaded and barbed transition, especially poly to brass to steel. Different materials move at different rates. |
| Valves and the fill port | Valve stem packing, and the port used to charge the loop. One left not quite closed weeps for months. |
| Pressure and temperature ports | Easy to skip. A leaking P/T port drips just enough to matter without making a puddle. |
| Unit connections | Where the loop meets the heat pump, including coax connections and any service valve that was opened. |
Every one is a mechanical joint, reachable without a shovel.
Mineral staining is the tell, and also the trap
When loop fluid escapes and evaporates it leaves its minerals behind, building a chalky white crust. Find the crust and you have found the leak. I am not smarter than the last technician, I am reading the residue.
A slow enough weep never leaves a stain. If fluid comes out a bead at a time and evaporates off a warm surface, there is nothing to see. The leak is real, pressure keeps dropping, and the evidence never forms. So the answer becomes add more fluid, and the joint never gets touched.
The one real exception: older pipe with push together fittings
There is a case where the leak genuinely is below ground, and even then the pipe wall is not what failed.
Older loops used the older style poly pipe and were assembled with push together fittings rather than fused joints. Pipe in the ground expands and contracts through the seasons, and that movement works on a push together joint year after year until it cracks or pulls apart. So even the underground exception is a fitting failure caused by thermal movement, not polyethylene wearing out.
Those are the hardest to find: buried in soil, a slow weep leaves no staining anybody will see.
When it really is underground, blame a person or a beaver
Of my three, two I found. One I never did, and I would rather say so than pretend otherwise.
One I found was a pond loop. Fixed it, and a beaver chewed into it. Fixed it again, and the same beaver chewed straight back in. The homeowner finally trapped him and relocated him, and that loop has been quiet ever since. It makes an honest point: when a buried loop does lose fluid, the cause tends to be external and unusual, not the technology failing.
Otherwise, actual poly leaks come down to homeowner or technician error: the loop was never pumped up properly, or never sealed properly. That is workmanship, not product.
Never put sealer or stop leak in a geothermal loop
If anybody offers to pour stop leak into your loop, say no. That is a rule, not a preference.
Sealer cannot fix what is actually broken. A weeping flange gasket or a cracked fitting is a mechanical problem, and no additive tightens a joint. Worse, it does not stay where the leak is. It circulates through the flow center, the pumps, and the heat exchanger, which are the expensive components and exactly the ones you do not want coated or restricted. A bottle of sealer is a second problem on top of the first.
What all that topping off is really costing you
Adding fluid every season only looks cheap because each visit is small.
Every refill drifts the antifreeze concentration, because what leaked out and what goes back in are rarely the same. Air gets introduced with the fluid, and a pump fed air cavitates, runs loud and wears out early. Flow drops, the heat pump loses capacity and efficiency, and the power bill climbs for reasons nobody connects to a weeping fitting.
Then the part that bothers me most. The homeowner decides geothermal is unreliable and tells the neighbors. The actual defect was a gasket.
This is the whole argument in one job
A loop that was never pumped up right is the same argument: the technology does not need to get better, the technicians working on it do.
A technician who has only worked on air source equipment walks into that mechanical room without a mental list of where a loop leaks. Flow center gaskets, hose kit o-rings, P/T ports and fill valves are not on his map, because none of that exists on the equipment he trained on. So he does the thing he knows, puts fluid back in and leaves. He is not lazy, he has never been shown where to look. That is why geothermal repair is worth insisting on somebody who does geothermal, and why I carry the IGSHPA accreditation.
What I do about it
Pressure test it, find it, fix it. Not top it off and drive away.
The loop gets isolated and put under a pressure test, which separates an above ground problem from a buried one before anybody talks about digging. Then I go through the list above with a light. The repair is an o-ring or loop repair, a flow center replacement, a loop fill kit with a check valve so it stops taking on air, a loop flush, and a correct repressurization and seal.
Diagnosing an existing geothermal system is my Geothermal Diagnostic, $348 flat, at any hour, with a written report and a quote before I leave. The repair gets quoted after I know what is wrong, because quoting it before finding it would be guessing.
Questions I get about this
Why does my geothermal loop lose pressure?
Nearly always a mechanical joint above ground, not the buried pipe. Flow center gaskets, hose kit o-rings, threaded fittings, valve stems and the fill port are the usual suspects.
Can a buried geothermal loop leak?
Yes, but it is rare. In forty seven years I have had three. Modern loop pipe is heat fused into one continuous piece, so there is no joint down there to fail. The exception is an older loop with push together fittings, cracked by seasonal expansion and contraction.
How do you find a geothermal loop leak?
A pressure test first, which separates an above ground problem from a buried one. Then an inspection of every mechanical joint, looking for mineral staining. A very slow weep leaves no stain, which is why these get missed.
How much does it cost to find a geothermal loop leak in Kingfisher Oklahoma?
My Geothermal Diagnostic is $348 flat, the same price at any hour, with a written report and a quote before I leave.
Keep going:
Stop refilling it and let me find it
If somebody has been topping off your loop season after season, that is not maintenance, it is an unfound leak. I will pressure test it, go through every joint in that room, and tell you what is wrong. Geothermal is statewide Oklahoma for me, not just my daily service counties.
Dave Hartzell, Hartzell's Heat & Air, 602 S Main St, Kingfisher, Oklahoma. Master HVAC License, NATE Certified, IGSHPA Accredited. 47 years in the trade, 15+ years in business. The $348 flat Geothermal Diagnostic applies at any hour, no credit and no refund. A quote on a brand new system costs nothing.