Why is there water under my heat pump?
Short answer
Water under an air-source heat pump is often normal condensate, not a refrigerant leak. The outdoor coil gets very cold, so moisture in the air condenses on it and drains away. The problem is when water has nowhere suitable to go, pools against the building, freezes around the unit or causes persistent damp.
Last checked 24 September 2026 · 1 source
Why does a heat pump make water?
The outdoor coil can be colder than the surrounding air.
Moisture then condenses on the coil in the same way water forms on the outside of an iced drink.
During cold weather, frost can also build on the coil. The heat pump periodically runs a defrost cycle, which can produce a noticeable amount of water as the frost melts.
Where should the water go?
That depends on the unit and site.
Common solutions include a condensate tray, drain, gully or soakaway. The important point is that water should be managed so it does not create damp, ice or a slip hazard.
The source inspection found a unit with water collecting underneath and no obvious route to a drain. The installer’s view was that it should have been collected and routed away.
When should I worry?
Get the system checked if:
- water is entering the building;
- the area stays persistently saturated;
- ice builds up around the unit;
- the unit is not level;
- water appears to come from indoor pipework or valves;
- you see an error code or loss of heating performance.
A refrigerant leak will not normally look like a puddle of clear water under the outdoor unit.
Can pooling water cause mould?
It can contribute to damp conditions if water repeatedly sits against walls, paving or other materials.
That is why drainage is part of a tidy, durable installation rather than just a cosmetic detail.
What should I do next?
Check the manufacturer’s installation instructions and ask your installer to identify the intended condensate route. If there is no proper route, ask for the drainage to be corrected.
Sources
- Source interview with Heat Geek installer, condensate inspection section.
Last checked: 24 September 2026