Heat Pump Leaking Water: Where It Comes From and What to Do

Water pooling outside during winter is usually normal. Water anywhere near the indoor unit is not, and one cause accounts for most of it.

Start by deciding: indoor or outdoor

These are different problems with different urgency, and treating them as one question is why people worry about the harmless case and ignore the expensive one.

Where the water is	Usual meaning	Urgency
Under the outdoor unit, in winter	Melt water from normal defrost cycles	Normal, unless it is refreezing
Under the outdoor unit, in summer	Condensate, in humid weather	Normal in cooling
Around the indoor unit or air handler	Condensate that is not draining	Act now, this causes damage
Dripping from a ceiling below the air handler	Overflowing drain pan	Urgent
Dripping from an indoor mini split head	Blocked drain line or a sloping fault	Act now

The short version: outdoor water is usually the system working. Indoor water is the system failing to get rid of water it always produces.

Water outside the unit

A heat pump produces water as a matter of course. In cooling it condenses moisture out of indoor air. In heating it collects frost on the outdoor coil and then melts it off during each defrost cycle. That melt water has to go somewhere, and a puddle underneath is where it goes.

When outdoor water is a problem:

• It is refreezing into a growing slab. This is the important one. If melt water cannot drain away from the base, it refreezes and the ice column builds upward until it reaches the coil. The defrost cycle then loses ground every time it runs. Units in snowy climates belong on a raised stand for exactly this reason, and it is covered in why ice keeps building up.
• The volume is far beyond normal. Continuous heavy water in mild weather is worth a look.
• It is running toward the house rather than away, which is a grading problem that will eventually reach a foundation.

Water inside: the condensate drain

The indoor coil condenses moisture out of the air, that water collects in a drain pan, and the pan drains away through a line. Almost every indoor leak is a failure somewhere in that chain, and the most common failure by a wide margin is the simplest one.

1. A clogged drain line. Biological growth builds up inside the line over time until water cannot pass. The pan fills, then overflows. This is by far the most frequent cause and it is within normal homeowner maintenance to clear.

2. A full or failed condensate pump. Where the drain cannot run downhill, a small pump moves the water. If it fails, the pan fills.

3. A cracked or rusted drain pan. Older systems, and the reason a secondary pan exists on attic installations.

4. A frozen indoor coil that is now melting. Restricted airflow from a dirty filter can freeze the indoor coil in cooling. When it thaws it produces far more water at once than the pan is designed to handle. If you find ice on the indoor coil, the leak is a symptom and the airflow is the cause.

5. Disconnected or poorly sloped drain line. Frequently a workmanship issue that appears soon after installation or service.

6. A blocked mini split drain. On a wall-mounted head the drain runs through the wall penetration. A blockage or a line that has been kinked or lifted sends water back into the unit and down the wall.

Why the system may shut itself off instead

Many systems have a float switch in the drain pan that cuts the whole system off when the water level rises. That is deliberate: it is cheaper to lose cooling than to lose a ceiling.

This produces a symptom that looks nothing like a leak. The system simply refuses to run, the thermostat appears fine, and nothing obvious is wrong. If your system has stopped dead and you have not looked in the drain pan, look there, because a full pan will keep it off no matter what you do at the thermostat. The full sequence is in the not-turning-on checklist.

Until the water level drops, the system stays off. Clearing the drain resolves both the leak and the shutdown at once.

What to do right now

1. Switch the system off if water is reaching anything it should not. Continuing to run it produces more water.
2. Check and change the filter. Restricted airflow is behind the frozen-coil version of this problem, and it costs nothing to rule out.
3. Look in the drain pan. Standing water confirms a drainage problem rather than a refrigerant one.
4. Clear the drain line. A wet vacuum at the outdoor termination point is the usual homeowner method, and clearing a blocked condensate line is routine maintenance rather than a repair.
5. Check the line has continuous fall and has not been kinked or lifted by anything.
6. Do not simply reset a float switch and carry on. It tripped for a reason, and overriding it is how ceilings get damaged.

Call a technician if the coil is icing repeatedly with a clean filter, if the pan is cracked, if a condensate pump has failed, or if clearing the line does not resolve it. Repeated indoor coil freezing with good airflow can indicate low refrigerant charge, which needs an EPA Section 608 certified technician because it means a leak.

Preventing the next one

This is one of the few faults that is genuinely preventable with routine attention.

• Flush the condensate drain annually, before cooling season. This single task prevents most indoor leaks and most float-switch shutdowns.
• Change filters every one to three months. Airflow restriction is the root of the frozen-coil pathway.
• Ask for the drain to be checked at every service visit. It is on any reasonable maintenance checklist, and our maintenance cost guide covers what else should be.
• On attic installations, confirm a secondary pan and overflow switch exist. They are the difference between a puddle and a ceiling repair.

Common questions

Is water under my heat pump in winter normal? Usually yes. Each defrost cycle melts frost off the outdoor coil and that water drains underneath. It becomes a problem only if it cannot drain away and refreezes into a growing mass of ice around the base.

Can I just empty the drain pan and carry on? Only as a stopgap. The pan filled because the water could not leave through the drain, so emptying it treats the symptom. Clear the line, otherwise it fills again within days.

Why did my system stop working when the only problem was water? Because of the float switch, which shuts the system down deliberately when the pan fills so that water does not overflow into the building. It is protection working, not a second fault.

Could a leak be refrigerant instead of water? Refrigerant leaves as a gas, so it does not pool. Visible liquid is water in essentially all cases. Refrigerant leaks show up as declining capacity, icing and eventually a compressor at risk, which is a different diagnosis entirely.

How this guide is put together

Indoor and outdoor water are treated separately because they have almost nothing in common: one is usually condensate management, the other is usually normal melt. Causes within each are ordered by how often they turn out to be the answer.

• Sources. Manufacturer documentation, industry pricing surveys and the references linked at the foot of this page.
• The DIY line. Anything involving refrigerant is legally restricted to an EPA Section 608 certified technician. Sealed systems, capacitors and line-voltage wiring are called out as technician work rather than left ambiguous.
• Prices. Given as ranges, because regional labour rates and local competition move them more than any other factor. Confirm against written quotes.

Sources

Primary references for the figures and procedures on this page. Where a number here is a range drawn from field experience rather than a published measurement, it is labelled as such in the text.

• EPA Section 608 Technician Certification — The federal requirement governing refrigerant handling, relevant where repeated coil icing indicates a leak.
• ENERGY STAR: Air-Source Heat Pumps — Federal efficiency criteria and general maintenance guidance for residential systems.
• AHRI Directory of Certified Product Performance — Confirm the certified specification of your matched indoor and outdoor units.

Last checked September 2026. Procedures are general to residential systems; confirm against the manual for your model.