In mid-September, most Ruston homes are still running the air conditioner, and heating season is weeks away. That makes now a good time to learn what normal looks like, so a heat pump not heating the way you expect later this fall does not catch you off guard. Here is how to tell normal behavior from a real fault the first time you switch to heat.
What Normal Heat Pump Heating Feels Like
A heat pump moves heat from the outdoor air into your home instead of burning fuel. ENERGY STAR describes a ducted air-source heat pump as a central air conditioner that also works in reverse. In heating mode, the outdoor coil absorbs heat and the indoor coil releases it.
So the air at your vents feels warm but not hot. A gas furnace delivers hotter air in shorter bursts, while a heat pump delivers milder air over longer run times. That air can feel lukewarm against your hand, even while the house is warming up.
Long, steady cycles are normal, and lukewarm air alone is not a heat pump not heating problem. Our heat pump repair and maintenance page covers the service side.
Defrost Cycles: The Steam, the Silence and the Whoosh
On cold, damp mornings, frost forms on the outdoor coil. A frosted coil cannot pull heat from the air, so a control board runs a defrost cycle. It briefly switches the system into cooling mode, sending hot refrigerant to the outdoor coil to melt the frost. Here is what you notice:
- The outdoor fan stops: the compressor keeps running, but the fan pauses so the coil warms faster.
- Steam rises off the unit: melting frost turns to vapor that can look like smoke.
- A whoosh or hiss: the reversing valve shifts the refrigerant flow at the start and end of defrost.
- Cooler air indoors: the backup heat strips often come on to temper the air.
A normal defrost usually lasts a few minutes, and then the fan restarts and heating resumes.
Auxiliary Heat and Emergency Heat Are Not the Same
Many ducted heat pump systems include electric resistance heat strips in the indoor air handler. The thermostat turns them on automatically as auxiliary heat, often shown as "AUX" on the display. That usually happens on the coldest mornings, during defrost, or after a big setpoint change.
Emergency heat is a manual setting. It locks out the outdoor unit and runs only the heat strips, or the furnace on a dual-fuel system. Use it when the outdoor unit has failed or is iced over while you wait for a technician.
It is not meant for everyday heating, because resistance strips use much more electricity than the heat pump for the same warmth. Our emergency heat page explains when this setting helps.
Why a Heat Pump Not Heating Usually Traces to a Few Faults
When the vents blow cool air, or the house keeps losing ground, one of these mechanisms is usually behind it.
- Stuck reversing valve: this valve routes refrigerant one way for cooling and the other way for heating. If its solenoid coil fails or the slide sticks, the system keeps cooling while the thermostat says HEAT.
- Low refrigerant from a leak: refrigerant circulates in a sealed loop, so a low charge means a leak. Heat output drops and the outdoor coil may frost unevenly.
- Coil iced solid: light frost is normal, but ice that never clears points to a failed defrost control board or a bad coil sensor.
- Failed outdoor fan motor: without airflow across the coil, the unit cannot absorb heat and ices up quickly.
- Thermostat misconfigured: the O/B setting tells the thermostat when to energize the reversing valve. Set wrong, heat and cool swap. A missing aux setting leaves you without backup heat.
- Tripped heat strip breaker: the house stays comfortable on mild days but falls behind on the coldest mornings.
If the trouble started after a thermostat swap, our thermostat service page covers setup and wiring checks.
A Ruston Scenario You Might Recognize
Picture a family whose heat pump cooled the house all summer, and who installed a new smart thermostat in August. On the first chilly night this fall, they switch it to HEAT. Both the indoor fan and the outdoor unit run, but the vents blow cool air, and an hour later the house is colder.
There is no frost on the outdoor coil and no tripped breaker. The air blowing out the top of the outdoor unit feels warm, the way it does in summer. That pattern says the system is working but moving heat in the wrong direction.
The first suspect is the O/B setting on the new thermostat. If that is correct, the next suspect is the reversing valve or its solenoid coil. This heat pump not heating case is a direction problem, not a capacity problem.
What You Can Check Safely Before You Call
A few checks narrow down the cause of a heat pump not heating, and none of them require tools.
- Mode and setpoint: confirm the thermostat is on HEAT and set above room temperature, with the fan on AUTO. A fan set to ON keeps blowing between cycles, and that air feels cool.
- Air filter: a clogged filter chokes airflow. The ENERGY STAR maintenance checklist recommends inspecting filters once a month.
- Outdoor unit: make sure the fan spins, and clear leaves and pine straw away from the base.
- Frost pattern: a thin, even frost that clears on its own is normal. Thick ice over the whole coil, or frost on only part of it, is not.
- Breakers: check the breakers for the outdoor unit and the air handler, since heat strips often have their own breaker.
Safety Notes
- Leave the ice alone: do not pour hot water on the outdoor coil or chip ice with a tool. One puncture in the thin tubing releases refrigerant.
- Cut power before clearing debris: switch off the outdoor disconnect first, and do not open the unit's electrical panel.
- Reset a breaker only once: if a heat pump or heat strip breaker trips again, leave it off and call.
- Smoke or burning smells: a faint dusty smell the first time the heat strips run each fall can be normal. Real smoke or a hot electrical smell is not, so turn the system off, get everyone out and call 911 from outside.
- Gas smell or CO alarm: on a dual-fuel system with a gas furnace, leave right away and call the gas utility's emergency line or 911 from outside.
- Refrigerant needs certified hands: under EPA Section 608, technicians who service refrigerant systems must be certified.
When to Call a Professional
A heat pump not heating after these checks needs a technician. Call when the air stays cool in HEAT mode after you have confirmed the thermostat settings, or when ice covers the outdoor coil and does not clear after several defrost cycles. Other signs include an outdoor fan that sits still while the compressor runs, AUX showing nearly all the time on mild days, and a breaker that trips twice.
If you switch to emergency heat to stay warm, treat it as a stopgap until the outdoor unit is repaired. Low refrigerant means a leak, and the EPA's refrigerant program governs who may handle that work. The heating team at Mark Johnson & Sons Plumbing works on heat pumps, thermostats and backup heat.
Frequently Asked Questions
Why does my heat pump blow cool air for a few minutes on cold mornings?
That is usually a defrost cycle. The system briefly switches to cooling mode to melt frost off the outdoor coil, and aux heat often softens the effect.
Should I use emergency heat when it gets cold?
Not as a routine setting. Aux heat already comes on automatically when needed, so save emergency heat for an outdoor unit that has failed or iced over.
Is a heat pump not heating on the coldest mornings a sign of failure?
Not necessarily. Heat output drops as the outdoor air gets colder, which is why aux heat exists. If the house falls behind even with AUX showing, check the heat strip breaker, then call.
Plan Your First Heat Check This Fall
When evenings in Ruston finally turn cool later this fall, run a short test on HEAT before you need it. If something seems off, write down what the thermostat displays, whether the outdoor fan spins, what any frost looks like and whether a breaker has tripped.
Send those details through our contact page or book a time online, and Mark Johnson & Sons Plumbing can help you sort out a heat pump not heating problem before the coldest weather arrives.