Repairing or Replacing a Failed Geothermal Ground Loop
Geothermal ground loops are among the most durable parts of a ground-source heat pump system, and true loop failure is uncommon. When performance drops, the cause is far more often in the indoor unit, pump, controls or flow than in the buried pipe, so diagnosis comes before any digging.
How does a loop problem show up?
Symptoms are indirect. Entering water temperatures drift outside the normal range, the heat pump trips on low or high pressure, heating output falls in late winter or cooling falls in late summer, or the system needs frequent antifreeze or water top-ups. A pressure that keeps dropping in a closed loop suggests a leak.
Many of these have simpler causes: trapped air, a failing circulation pump, a dirty strainer or a partly closed valve. Start with the checks in the geothermal heat pump maintenance guide before assuming the ground loop is damaged.
How is a loop fault diagnosed?
- Review monitoring or service history for trends in loop temperatures and pressures.
- Check pump operation, flow rate and heat exchange across the unit.
- Pressure-test the loop, which can show a leak without exposing any pipe.
- Locate the leak, where possible, by isolating sections of the header or individual circuits.
- Inspect the indoor connections and fittings, where most leaks actually occur.
The loop type matters. Horizontal fields, vertical boreholes and pond loops each fail and get repaired differently, as described in horizontal versus vertical ground loops. A design that is undersized can mimic a failing loop, so ask whether the original design matches the load.
What does repair involve?
Fusion-welded polyethylene pipe is designed to last for decades, and the weak points are fittings, joints and headers rather than the pipe. Repairs may be as simple as replacing an indoor fitting or a header connection. Where a leak is in a buried horizontal run, excavation to the fault may be required. In a vertical borehole, a damaged U-bend cannot usually be reached, so the circuit is often isolated and abandoned while the remaining loops carry the load, if the design had spare capacity.
Ground temperature and field size set what is possible. The Drake Landing borehole field, described on the borehole storage page, used 144 boreholes of about 35 metres, which shows how a field can be split into many parallel circuits. Residential geothermal systems are far smaller, but isolation by circuit follows the same logic. See also drilling depth and spacing.
When is full replacement considered?
Full replacement is rare and expensive. It may come up when several circuits have failed, when the field was badly undersized from the start, when freezing damaged piping or when the site changed, for example after construction over a horizontal field. Costs vary widely by region, soil, access and loop type, and only written site-specific quotes mean anything.
Compare the repair option, a partial new loop and replacement of the whole system. The lifetime picture in ground source heat pump lifespan helps, because the indoor unit may be nearing its own end of life.
Who should you call and what should you ask?
Start with the installer or designer of the system, then a qualified geothermal contractor who holds the relevant certification in your province. Ask whether the original loop design report and as-built drawings exist, since they show circuit layout and locations. Ask for a written diagnosis, a pressure-test result and options with a price for each.
- Where exactly is the problem, and how was it confirmed?
- Is the loop warranty or installer guarantee still valid?
- Could the cause be flow, antifreeze concentration or the indoor unit?
- What is the plan if the repair fails?
If financing or rebates are part of the picture, check geothermal rebates and financing for how to confirm current terms.
What can owners do to avoid loop trouble in the first place?
Prevention is mostly about records and routine. Keep the original design report, a sketch of where the loop sits and the commissioning readings from the first year. Note the normal loop pressure and temperatures in a logbook and compare them each season. Slow drifts are easy to spot on paper and hard to notice otherwise.
Protect the ground above any horizontal loop from heavy construction, deep digging and tree planting. Call before any excavation near the field, and mark the header location. Make sure the antifreeze mix and its concentration are checked at service visits. A loop that is looked after tends to stay quiet for decades.
Quick answers
How long does a geothermal ground loop last?
Properly installed polyethylene loops are commonly expected to last several decades. The indoor heat pump unit usually wears out first.
Can a geothermal loop leak be fixed without digging up the yard?
Sometimes. Leaks at indoor fittings or headers need no excavation, and failed boreholes can often be isolated. A leak in a buried horizontal run may require digging.
Is a drop in performance always a loop problem?
No. Flow problems, trapped air, pump issues, undersizing and indoor unit faults are more common. A pressure test and a service check should come first.