Here's how it usually goes in Tampa: the heat pump runs in cool mode for eight months straight, nobody gives it a second thought, and then the first cold night of the year hits. You flip the thermostat to HEAT, the vents blow lukewarm — or flat-out cold — and the house never warms up.
Good news first: about half the time, nothing is broken. Heat pumps heat differently from furnaces, and two of their normal behaviors look exactly like failures. The rest of the time, the fixes are specific and diagnosable. Here's how to tell the difference.
How a heat pump actually heats your house
A heat pump doesn't make heat — it moves it. In summer it pulls heat out of your house and dumps it outside. In winter a part called the reversing valve flips the flow: the outdoor coil pulls heat out of the outside air (yes, even 45° air holds heat) and carries it inside. That's why heat pumps move $2–$4 of heat for every $1 of electricity — no furnace can do that.
Two quirks come with the design. On cold, damp nights, frost builds on the outdoor coil, so every so often the system runs a defrost cycle — it briefly switches back to cool mode to melt the frost, and the indoor vents blow cool air for 10–15 minutes. And when the pump can't keep up alone, backup heat strips (your AUX heat) kick in to help. Both are normal. Both get mistaken for breakdowns every single fall.
Five checks before you call
Run these first — they're free
- Thermostat on HEAT, fan on AUTO. Sounds basic; it's the #1 finding on no-heat calls. If the fan is set to ON, it blows unheated air between cycles and feels like cold air.
- Bump the temperature up 3–4 degrees and wait 30 minutes. If you caught it mid-defrost, it needs time to finish and recover. Judge it after half an hour, not two minutes.
- Check the air filter. A clogged filter strangles airflow in heat mode just like cool mode — weak, lukewarm air at every vent.
- Look at the outdoor unit. A light, even frost is normal. A unit encased in ice, or buried in leaves and mulch, is not — clear the debris, and if the ice is thick, call us.
- Check the breakers. The outdoor unit and the air handler usually have separate breakers. A tripped one means the handler may blow air the pump never heated.
When it blows cold and it's NOT normal
If the checks pass and the air stays cold, the short list of real causes is: a reversing valve stuck in cool mode (the system literally air-conditions in January), low refrigerant (the pump can't gather enough heat to move), a failed defrost board or sensor (the coil ices over and chokes), dead backup strips (fine at 50°, miserable at 38°), or a thermostat that's wired or configured wrong for a heat pump. Every one of those is a find-it-and-fix-it repair — none of them automatically means a new system.
A no-heat call, to me it seems suspicious when…
…the thermostat says AUX all morning on a 55° day. That means the strips — the expensive backup — are carrying the house while the heat pump sits there doing nothing. Folks pay that power bill for weeks before they call. If your AUX light lives on, that's the call to make. — wil, owner
When it's time to call
Call when the air stays cold past 30–45 minutes, when the outdoor unit is a block of ice, when AUX runs all day, or when the house temperature keeps sliding instead of holding. Heat problems in Tampa don't fix themselves, and the second cold night is always colder than the first. Same-day estimates are free — we'll tell you straight whether it's a valve, a charge, or just a defrost you caught mid-cycle.
Questions Tampa homeowners ask us
Why is my heat pump blowing cold air?
Sometimes it's normal: during a defrost cycle the system briefly runs in cool mode to melt frost off the outdoor coil, and the air feels cool for 10–15 minutes. If the air stays cold for an hour or more, the reversing valve may be stuck in cool mode, the refrigerant charge may be low, or the backup heat strips may not be kicking in. That's a repair call, not a settings problem.
Why is steam coming off my outdoor unit?
That's the defrost cycle melting frost off the coil — the steam looks alarming but it's the system working correctly, and it should stop within about 15 minutes. Worry when the unit is encased in thick ice for hours and never clears. Solid ice usually means the defrost control or sensor has failed.
What does AUX heat mean on my thermostat?
AUX means your backup electric heat strips are running. They switch on during defrost and on the coldest nights to help the heat pump. They cost roughly three times more per hour than the heat pump itself, so a little AUX is fine — but if your thermostat shows AUX all day on a mild Tampa day, the heat pump isn't doing its job and you're paying strip prices for all your heat.
Can a heat pump keep up with Tampa winters?
Easily. Tampa's cold snaps are mild by heat pump standards — most winter nights stay in the 40s and 50s, right in a heat pump's efficient range. A properly sized heat pump heats a Tampa home without leaning on the backup strips except during defrost and the rare hard freeze.
Should I switch my thermostat to Emergency Heat?
Only if the outdoor unit has completely failed and you need heat while you wait for us — Emergency Heat runs the backup strips full-time, which is the most expensive way to heat your home. It's a limp-home mode, not a fix. If the outdoor unit still runs at all, leave it on HEAT and call us.
Heat pump acting up? AC shut off on you?
Same-day service across Tampa — and same-day estimates are free. Call (813) 770-2722 or request service online.
Keep reading: Heat Pump vs Straight Cool: What's Best for Tampa? · Heater Not Working? Tampa's First-Cold-Night Playbook