Frozen Heat Pump? What the Ice Means

A little frost is normal

Walk past your outdoor heat pump on a cold morning and you may find it wearing a coat of frost. In winter that’s expected. A heat pump pulls warmth from outside air, which chills the coil below freezing, and moisture in the air condenses and freezes on it. The system is built for this.

To clear it, the unit runs a defrost cycle: it briefly reverses, sends warm refrigerant out to the coil, and melts the frost away. You might see steam rising off it, hear a whoosh as it switches, and feel cooler air indoors for a few minutes. All of that is the system working as designed.

When ice is a problem

The trouble sign is ice, not frost. If the coil is buried in a thick, solid block, if the top of the unit is capped with ice, or if it stays frozen for hours and never clears, something is wrong. A healthy heat pump frosts and defrosts on a cycle. One that’s iced over solid has lost that rhythm.

A few things cause it. Low refrigerant keeps the coil too cold and defrost can’t keep up. A failed defrost sensor or control board means the cycle never triggers. A stuck reversing valve can’t send warm refrigerant to the coil. And a fan motor that isn’t spinning lets ice build with nothing to move air across it.

There’s also the simple stuff. If the unit sits low and snow drifts around it, or ice from a roofline drips and refreezes on top, airflow gets blocked and ice accumulates. Keep at least a foot and a half of clearance on all sides and knock down drifts after a storm.

What you can safely do

If you find the unit iced over, switch the system to emergency heat at the thermostat so your backup keeps the house warm, and turn the heat pump itself off. You can pour warm, not boiling, water over the coil to melt the ice. Never chip at it with a tool, since the coil fins bend easily and a puncture means an expensive repair.

Once it’s clear, switch back and watch whether it frosts and defrosts normally. If it ices up again within a day, the defrost system or refrigerant charge needs a professional look.

When to call

Occasional frost that clears on its own needs nothing from you. Ice that keeps coming back, a unit that runs constantly without defrosting, or a coil that won’t clear all point to a fault worth diagnosing before it strains the compressor.

Boulder’s freeze-thaw winters are hard on outdoor equipment, and a heat pump that ices repeatedly is telling you something. If yours does, call us and we’ll find out why.