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Heat Pump Repair Fairfax VA: Why Is My Heat Pump Not Heating?

Some heat-pump “no heat” calls are actually normal behavior, gentler 90–95°F supply air and a brief defrost cycle. The real faults are a thermostat setting, a clogged filter, low refrigerant, a stuck reversing valve, a dead outdoor unit, or backup heat not engaging. An honest guide for Fairfax homeowners.

Fairfax Mechanical Team·September 25, 2026·10 min read

Cold-climate heat pump outdoor unit on a concrete pad in a frost-covered suburban backyard on a gray winter morning, heat pump not heating in Fairfax VA

A heat pump not heating is usually caused by a thermostat setting issue, a clogged air filter, a normal defrost cycle (temporary), low refrigerant from a leak, a stuck reversing valve, a failed outdoor unit or fan, or backup heat not engaging in extreme cold. Some are simple checks; refrigerant, reversing-valve, and electrical problems need a technician.

First, rule out normal heat-pump behavior

Before assuming a breakdown, know that two things surprise Fairfax homeowners but are completely normal: heat pumps deliver gentler warm air (around 90–95°F) that can feel “lukewarm” compared to a furnace, and they run a defrost cycle in cold weather, briefly reversing to melt frost off the outdoor coil, during which vents blow cool air for a few minutes and steam rises off the outdoor unit. If your “no heat” is really just cooler-than-a-furnace air or a brief defrost, the system is fine.

The most common reasons a heat pump won't heat

1. Thermostat settings

Confirm it's set to “Heat,” the temperature is above the room reading, and the batteries are fresh. Avoid “Emergency Heat” unless the heat pump has actually failed, it bypasses the efficient heat pump and runs costly backup only.

2. A clogged air filter

Restricted airflow reduces heat delivery and can freeze the coil. Replace it first.

3. Constant cold air (not just during defrost)

If the heat pump never produces warm air, the common culprits are low refrigerant from a leak or a stuck reversing valve (the component that switches between heating and cooling). Both require a professional.

4. The outdoor unit isn't running

A heat pump extracts heat from outdoor air, so if the outdoor unit is off, due to a failed capacitor, contactor, fan motor, or a tripped breaker, it can't heat. A common electrical repair.

5. Iced-over outdoor unit

A little frost is normal; a unit encased in ice that never clears indicates a defrost-control failure and blocks heat production.

6. Auxiliary heat not engaging

In very cold Fairfax weather below the heat pump's balance point, backup (auxiliary) heat should kick in automatically. If it doesn't, due to a failed heat strip or control issue, the home can't stay warm.

Emergency Heat is not a fix

Switching to Emergency Heat will warm the house, but it runs only the electric resistance backup and bypasses the heat pump entirely, the most expensive way your system can operate. Use it as a temporary bridge on a cold night, not as a solution, and have the underlying fault diagnosed.

What you can safely check yourself

✓
Set the thermostat correctlyHeat, not Emergency Heat, with the temperature above the room reading and fresh batteries.
✓
Replace the air filterRestricted airflow reduces heat output and can freeze the coil.
✓
Note whether the cold air is brief or constantBrief points to a normal defrost cycle; constant points to a real fault.
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Check the outdoor unitConfirm it is running and clear of ice, leaves, and debris, with about two feet of clearance.
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Check the breakerA tripped breaker will stop the outdoor unit from running at all.

When to call for heat pump repair in Fairfax

If the outdoor unit won't run, the coil stays iced, the air is constantly cold, or backup heat isn't working, it's time for a professional. Refrigerant, reversing-valve, and electrical repairs aren't DIY, and running a struggling heat pump can worsen the damage.

90–95°FNormal heat-pump supply air, gentler than a furnace

15 minThe longest a normal defrost cycle should run

2 ftClearance the outdoor unit needs to draw heat

Why choose Fairfax Mechanical

We're an experienced, licensed Virginia HVAC contractor who works on heat pumps every day, separating normal winter behavior from real faults and fixing refrigerant, reversing-valve, defrost, and electrical problems correctly. We offer same-day heat pump repair across Fairfax, Vienna, Oakton, Burke, and all of Northern Virginia.

Heat pump not keeping up in Fairfax? Same-day heat pump repair across Northern Virginia.

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Frequently Asked Questions

Why is my heat pump not heating in Fairfax, VA?

A heat pump not heating is usually caused by a thermostat setting issue, a clogged air filter, a normal defrost cycle (temporary), low refrigerant from a leak, a stuck reversing valve, a failed outdoor unit or fan, or backup heat not engaging in extreme cold. Some are simple checks; refrigerant, reversing-valve, and electrical problems need a technician.

Why does my heat pump blow air that feels only lukewarm?

Because that is how heat pumps are designed to work. A heat pump delivers a steady, gentle supply of warm air around 90–95°F, while a gas furnace delivers a hot blast around 120–140°F. The heat pump is still heating your home efficiently, it simply moves heat rather than creating it by combustion, so the air feels milder at the register.

Is steam coming off my outdoor unit normal in winter?

Yes. During a defrost cycle the heat pump briefly runs in cooling mode to melt frost off the outdoor coil, and what you see rising off the unit is water vapor from that melting frost. It is completely normal, lasts a few minutes, and ends on its own. Constant cold air inside the home, however, is not normal.

Should I use Emergency Heat on my Fairfax heat pump?

Only if the heat pump has actually failed. Emergency Heat bypasses the efficient heat pump entirely and runs only the expensive electric resistance backup, which can dramatically raise your Dominion Energy bill. If your heat pump is simply running a defrost cycle or delivering lukewarm air, Emergency Heat is the wrong setting.

Does Fairfax Mechanical repair heat pumps in Fairfax, VA?

Yes. Fairfax Mechanical services and repairs heat pumps across Fairfax, Vienna, Oakton, Burke, Mantua, Fairfax Station, and all of Northern Virginia, including refrigerant, reversing-valve, defrost, and electrical repairs.

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