Florida does not get real winters, but the handful of genuinely cold nights we do get every year produce a very specific service call: "my heat pump is not heating." Sometimes that is a real problem. Just as often, the system is doing exactly what it is designed to do and the confusion is about what a heat pump is actually supposed to feel like compared to a furnace.
First, What "Normal" Heat Pump Heat Actually Feels Like
Most Florida homes have never owned a gas furnace, so there is no baseline for comparison. A heat pump supplies air around 95-105°F at the vent — noticeably warm to the touch, but nowhere near the 120-140°F a gas furnace produces. If the air feels "warm but not hot," that is likely correct operation, not a malfunction. Check the thermostat is actually reaching its setpoint over time before assuming something is wrong.
1. Defrost Cycle (Usually Normal, Not a Malfunction)
On cold, humid nights, frost can form on the outdoor unit's coil — ice buildup blocks the coil's ability to absorb heat from outdoor air. To clear it, the system periodically reverses into a brief cooling cycle (5-10 minutes) that melts the frost, during which indoor vents blow noticeably cool air. This is standard, engineered behavior on every heat pump, not a defect.
How to tell it's the defrost cycle and not a real problem: it is brief (under 15 minutes), the outdoor unit's fan may pause, and normal heating resumes right after. If cool air continues well past 15 minutes or happens on mild, non-frosty nights, move to the causes below.
2. Thermostat Set to the Wrong Mode
The same mode-mix-up we cover in our AC blowing warm air guide applies in reverse here — confirm the thermostat is actually set to HEAT, not COOL or FAN-ONLY, especially after a recent thermostat install or a schedule change.
3. Dirty Air Filter
A clogged filter restricts airflow across the indoor coil regardless of whether the system is heating or cooling, reducing output and potentially tripping a safety switch. In Florida's year-round-AC households, filters often get less attention once the weather cools — worth checking specifically before winter's occasional cold snaps.
4. Failed Reversing Valve
The reversing valve is the component that lets a heat pump switch between cooling and heating mode by reversing refrigerant flow. If it fails or gets stuck, the system may only be able to run in one mode regardless of what the thermostat calls for — commonly presenting as "it cools fine but will not heat."
Fix: Reversing valve replacement, $400-$800, requires a licensed technician.
5. Low Refrigerant
Same underlying issue as in cooling mode — a heat pump extracts heat from outdoor air using refrigerant, and if the charge is low from a leak, heating capacity drops along with cooling capacity. Weak heating paired with weak cooling earlier in the year points here.
6. Failed or Undersized Auxiliary Heat Strips
Many heat pumps include electric auxiliary heat strips as backup for unusually cold conditions. If these fail, the system can still run in heat pump mode but will struggle to keep up on the coldest nights of the year, feeling noticeably weaker than usual specifically during cold snaps.
Fix: Heat strip element replacement, $150-$400.
Reversing valve and auxiliary heat strip checks are part of every Comfort Club fall tune-up — catching heating issues before the one or two genuinely cold weeks Florida gets each year. See Comfort Club plans.
When to Call a Tech
If you have confirmed the thermostat is set correctly, replaced the filter, and the system still is not producing warm air outside of a brief defrost cycle, the cause is mechanical and needs diagnosis. World Air HVAC services heat pumps across Tamarac, Fort Lauderdale, Coral Springs, Pompano Beach, Hollywood, Plantation, Sunrise, Davie, Miramar, and Deerfield Beach.
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